Being the semi-pessimistic/wordy person that I am, I'll cover two things: Games/franchises I love and games/franchises I hate.
Love:
Kingdom Hearts, Kingdom Hearts 2, and Kingdom Hearts: Chain of Memories: I only got to play those 3 in the series (sorry, not going to get 2-3 handhelds to play them all), but they're all really good games. I actually never got to finish KH2, but I certainly will eventually (plan to get a PS2 and all of the PS2-compatible KH titles I can).
Halo Franchise: I'll just name the whole franchise, but I wasn't that impressed with Halo 3, which felt like a step down with multiplayer when compared to Halo 2, and a redundancy of sorts (particularly the ending) from the first installment. Thinking about it, as great as the franchise is, they actually have 4 stellar titles (Halo: Combat Evolved, Halo 2, Halo: Reach, and Halo 4), one OK title (Halo 3), and 2 that were kind of stinky (Halo Wars and Halo 3: ODST, which I never actually got to play).
Gears of War franchise: I want to go beat the second and third games on Insane sometime, but I'm bad at replaying campaigns (part of why I hate the way they make you beat the campaign before playing Insane on Gears). I didn't care for the multiplayer after the first game, but it was a nice story, and one of the few games I can think of where there were plenty of well-developed characters, especially surprising because of the genre (shooter) that it was in.
Unreal Championship: This was THE PLACE to be on Xbox LIVE before Halo 2. It was where I started Xbox LIVE, and I wish that its successor (Unreal Championship 2: The Liandri Conflict) had been better and that console gamers had given Unreal Tournament 3 some love.
Forza 2-4: I didn't play the first, nor have I played Horizons, but I can definitively say that this is the best racing franchise there's ever been. I really liked Project Gotham Racing and a few of the Need for Speed games (specifically the original Most Wanted and Carbon), but Forza is the best that there is.
Pok?mon: I won't list all of the games that I've played in the franchise, but basically everything on Nintendo 64 was in my console at some point, and about everything from Blue to Sapphire made it to one of my handhelds.
Urban Terror: I'll just point this out as a standout PC shooter that I really liked. It started as a mod of Quake 3: Team Arena, but it's actually a standalone title you can download now. Even today, it's a pretty impressive game because of the need to bandage yourself when shot and the dynamic breath (depending on your remaining health). It was probably the first shooter I ever played, as well as the first competitive-style game I played online.
I'll stop that list there, as I could go one for a loooong time. Now, to the bad.
Hate:
Grand Theft Auto Franchise: I've only played GTA III and Vice City, while also seeing San Andreas played. I've never really figured out what makes these mind-numbing games so great for people. They seemed shallow, repetitive, and without much REAL direction. The open-world play is great and all, but it never felt like it served a great purpose.
Call of Duty: Modern Warfare 2-3: I have to be honest here, I poured a LOT of time into MW2, but after I got Black Ops, I realized how poorly-made that turd from Infinity Ward was. Then MW3 came out, and I was appalled at the fact that they managed to make something WORSE. Those two games are so bad that I'll never buy from Infinity Ward again.
Assassin's Creed 2: Honestly, the game's not that bad. It just didn't feel like the gameplay varied enough from the previous title, so it was rather bland and unimpressive. I'm now ignoring the rest of the games, despite owning Revelations and living with a cousin who has Brotherhood. I just have no desire to finish up the series right now.
BioShock 2: I loved the first game. This one? It's really chuggy and sad. I'm supposed to be a Big Daddy, yet I feel like glass. I get that part of the survival/horror FPS games is the scarcity of weaponry, but it's extremely annoying having to trudge through the game so slowly and constantly feel like you're about as strong as a Little Sister, rather than being a Big Daddy. I've been trying to force myself through the campaign, but I basically play for 30-60 minutes than take a 2-month break. Nothing is gripping in the story, the gameplay's slow and monotonous, and I just can't believe how irritated I get playing that game.
Anyway, I could add to both lists for hours, but I'll stop.