Technically the game ends at the end of Act IV when you kill Diablo. By now you’ve killed all of the other prime evils except for Baal who escapes at the end, (a pretty shitty ending.) Then, if you like wasting money, you can get the expansion and continue your pursuit of Baal.
After you beat Diablo and start act V you begin in the under siege Barbarian fort on Mt. Aareat. Your first order of business is to stop the immediate threat of the encroaching demon army and catapults outside the gates. The problems start the minute you exit the fort. Hope you like ugly earthworks with trenches, mounds, ,footbridges and bombed-out towns ‘cause that‘s what you‘ll be seeing for the next two hours. All of this fugly garbage in your way makes a sort of labyrinth that you have to zig-zag through. And while you’re doing this you have to fight about 500 trillion of the most bland enemy, over and over. Twenty minutes later nothing has changed and you start wondering, is this going to stop at some point? Please tell me there’s more than earthworks and spiny mole-men. The monotonous and seemingly endless onslaught is punctuated with you getting hit by a stupid catapult with unknown whereabouts. Almost all of the level is linear. With the exception of the hundreds of obstructions that you have to walk around, you walk from right to left. Any time you’re not in an ice cave, you’re walking in one direction like a sidescroller. Eventually you get past the front lines and are introduced to what is the most annoying enemy in the entire game. Prior to the expansion pack, the little fetish tiki men were by a wide margin the most aggravating enemy. But after that they lost the title to…
...Imps. They shoot fireballs and teleport. But that’s not all. They’re actually the most versatile enemy. They can climb up and attack you from siege towers as well as from atop these big things that look like Wargreymon. 
Often you can’t get within striking distance before they teleport off screen. Then they’ll teleport back on screen just to shoot fire at you again right before they leave once more. Sometimes they just teleport like five times in a row. You’ll be dealing with about 3-8 of them at a time. It’s too much of a pain in the ass to chase them all down individually because it just takes too long. Just accept the fact that you’ll be traveling with them and be getting hit with fireballs constantly throughout this area unless you have some kind of silver bullet spell to deal with them.
Often you can’t get within striking distance before they teleport off screen. Then they’ll teleport back on screen just to shoot fire at you again right before they leave once more. Sometimes they just teleport like five times in a row. You’ll be dealing with about 3-8 of them at a time. It’s too much of a pain in the ass to chase them all down individually because it just takes too long. Just accept the fact that you’ll be traveling with them and be getting hit with fireballs constantly throughout this area unless you have some kind of silver bullet spell to deal with them.
Speaking of spells there are some things about the new Druids spells that really suck. The three different types of spells he has are elemental, summoning, and shape shifting. In shape shifting you can turn into a werebear and a werewolf and also get subsequent spells to perform while in either form. The problem is that you lose the ability to use all of your other spells while you’re in that form. You soon realize that there’s really no advantage to changing forms. In fact it’s more disadvantageous because you can’t use your best offensive spells. So that’s a third of your spells that you’re not even going to use because there‘s no benefit to you. In the summoning spells there are various animals and other life forms you can bring forth to fight or heal you as you play. There are three different types of vines that do different things but you can only have one summoned at a time. That makes sense I guess since a necromancer can only have a single golem at a time too. The druid can also summon a wolf/wolves depending on how many times the spell is leveled up. Then later you learn to summon dire wolves which are different. When I first learned this I thought it was good because it meant that I could have a dire wolf summoned in addition to my two regular wolves, but no. You can either have dire wolves or regular wolves out, not both at the same time which is bullshit. If you’re a necromancer you get to have skeletons AND skeleton mages out. How is that any different? Then later you learn how to summon a bear. And I thought surely I could have a bear and wolves. I mean, abear is totally different right? Again it was no. You either get the bear or wolves. And what makes it worse is that you can only ever summon a single bear. Leveling it up only makes the bear stronger. This leaves you to ponder which is better to have, one supercharged bear or an army of wolves? Well I’m certainly never going to need regular wolves again. In fact all of the early spells for all of the characters are pretty much useless after you reach about level eighteen. They’re so weak in comparison to the later spells that it would take 10 level-ups for one to emulate the damage of the first level of a later spell. It’s annoying because you spend points leveling up spells that you’re basically going to throw away and never use again.
Another thing I don’t understand about the expansion is the inclusion of ethereal clothes and weapons. The only difference between ethereal things and non-ethereal things is that ethereal things can not be repaired and consequently break and become useless at some point. Also they technically have lower requirements to use than their non-ethereal counterparts but that’s just a shroud to hide the fact that they’re pointless.
At the end of act V you get to fight Baal, the Lord of Destruction. If I remember correctly Baal is the pagan god of rain. In the Bible the Jews and pagans were having a deity-off to see who’s god was more powerful. The challenge was making a bonfire. Whichever god made a fire first was the winner. Despite all of the dancing and self mutilation performed by the pagans, Baal didn’t respond. (I guess he was sleeping.) Then the Jews completely dowsed their pile of wood with gallons of water and adding insult to injury it exploded into flames. The pagans were at a huge disadvantage though. What made them think they could get fire from a rain god?
So now that Baal is the new boss of the game doesn’t that mean that he’s tougher to beat than Diablo? The answer is yes, a hell of a lot harder. Well it differs from character to character. If you’re an assassin you can just surround him with flame traps and then hide behind a rock and wait. When you first find Baal, he's sitting on his throne and you can't hurt him. He summons five waves of the most annoying enemies from each of the acts. It's really easy to be instantly surrounded and die before even getting to lay a hand on Baal. You end up having to run back through the labyrinth until the enemies are thoroughly separated and then hunt them down one by one. After the fifth wave of enemies Baal escapes through a portal. You follow him and then the real fight begins. His main attack seems to be a flame wake that is not only devastating to your health but impossible to dodge. And it pushes you far away making it really hard to get close to him. If you have any summoned creatures they should be immediately vaporized. Ultimately in order to hit him you have to take a hit. Needless to say you’ll be taking dozens of trips back to town for more health potions. Baal can also duplicate himself so that there are two of him. If you manage to kill his replicant it’s of no consequence to him. He doesn’t get hurt from it and he’ll just make another one. One hundred trips to town later the boss of Diablo II is dead. But does it really matter?
