I loved AC1, and started to love AC2 until they started making radical changes to characters and also changed the big monster battles.
I just about had it when I built up a couple of characters to get ability X, then have the entire skill tree not only revised, but the skills/abilities removed entirely from the character tree and transplanted into another.
Then, someone showed me how to get to this island with huge monsters on it. You could take them down at a reasonable level, but only if you joined fairly large hunting parties. Because of how groups could help each other out on the rebirth penalties when dealing tons of damage, you would get over the penalties pretty quickly. But then some developers decided that the big monsters weren't tough enough, and gave them super armor on top of their huge stacks of hit points. At that point, they were healing the damage I inflicted faster than I could inflict it.
It had a lot of weird but also interesting changes from AC1. Some of them, I really didn't like, but the game had other perks so I stuck with it. Whomever made the decision to keep rebalancing the game over and over again cause many, many more than just me to leave. Really dumb.
On the other hand - AC1 was my first MMORPG, and although very dated, my second favorite to this day. Stats were open ended, so if you figured out a way to jack them up by 100 points+ (potions + spells, etc), you could run like the roadrunner and jump on top of buildings. The physics system was fantastic.