Call of Duty. I LOVED Call of Duty. I spent hours playing United Offensive on-line as late as 2007. Finally, it seemed like it was me and maybe 30 other people who still did, and so I had to move on to Call of Duty 4.
I barely recognised the game. Their efforts to make it appeal to a larger target audience resulted in every server being filled with idiots who used grenades as their primary weapon and rocket launchers for a secondary. I missed the much more intuitive system in CoD:UO where American soldiers only used American guns, German soldiers used German guns, etc. and where they made you work like a dog to use things like artillery instead of getting lucky and having your grenade kill 5 people at once. There was none of this rank malarkey, you started off as a Pvt. every new round and had to work all over again from the same bonuses, which made more sense than levelling up so your nation won't be cheapskates and give you better weapons. "I'm sorry, we're not going to give you a better weapon until you kill X number of Germans, or happen to be on a team where they do kill many Germans. You see, we don't trust that we trained you well enough, so we're going to give you a shitty gun made of ass and recoil so you can go out and die."
Also, vehicles. You can brag about how CoD:WaW has tanks, but guess what? CoD:UO not only had tanks, but also jeeps and heavy tanks. It took the idiots who took over the franchise a long time to realise they maybe they should re-add 33% of the content everyone loved, but was cut out 5 years ago.
I could go on but I think I'll leave it there.