Ds2 is a great game, but it changed parts of the ds1 formula in ways that didn't go over well with fans. Most of the changes weren't bad, but it definitely gave the game a different feel. A few common complaints:

Dieing causes you to lose a portion of your max hp, down to 50% after enough deaths. You could reverse the hp loss by spending a consumable item or helping another player beat a boss. This one was unpopular because the game requires you to die to a boss enough times until you've mastered their moveset. Some people didnt like feeling punished for doing what the game expects them to do.

Enemies can only be killed a limited number of times before they permanently despawn. Having the game make itself easier if you failed at it enough felt insulting.

The dark souls combat system handles 1-on-1 fights better than fights against groups. Despite this, the game throws lots of group fights at you. Ds1 had a number of group fights as well, but you could lure the enemies out one at a time. In ds2, the enemy ai was changed so that enemies would chase you together.

There are a lot of great boss fights in the game, but there's also a lot of bland ones. A lot of the bland ones are giant dudes in a suit of armor with big two-handed weapons.

People liked how well connected the world of ds1 was. Not only could you see many of the upcoming levels in the distance, sometimes you could see the paths that connected them. Ds2 seems like it goes in the opposite direction and makes the world's geography impossible (and bizarre at times).