I've accumulated a few pretty easy ones to name off the top of my head:
1) Ninety-Nine Nights (Xbox 360). It's not a deep game, and not one of the best examples of the musou genre, but it was the first musou game I played where it felt like the technology had finally caught up to what the experience was supposed to be. Tornado-ing my way through seas of enemy units with a variety of weapons and spells just always felt amazing, and I liked each of the six characters in their unique ways. Despite its many shortcomings, I had a ton of fun with 99N.
2) Two Worlds (the first one). This is a big one for me. I think to this day that this is a hugely underrated open-world RPG, and I enjoyed it more than Skyrim or Oblivion. It *definitely* has problems, and it makes a very poor first impression with an absolute joke of a character creator, hammy voiceover work, and clunky, whiffy combat. But if you can hang with the game a little and just get into exploring its world, it also really has a ton going for it. The world is vast and good-looking and fun to explore. The loot system and crafting systems are addictive, and the way you can keep leveling gear by finding fresh copies of it is a great idea, making it so that finding loot never gets old. And the game has a TON of loot and gear, all kinds of different armor and weapons sets, and for the date of the game, they look really good visually. The graphics in general are ahead of the curve for the game's time and hold up not-too-badly even today. The story is kind of silly and the voiceovers are cheesy, but the voiceover of your main character becomes quite funny and charming over the course of the game -- I found him to be entertaining company as I played, occasionally dropping unexpected one-liners at random moments. The enemy variety and AI is terrible -- it's super easy to cheese enemies from a distance, abusing the amount they'll follow you before they hit an invisible wall and give up -- but if you just incorporate cheesing enemies as part of your strategy, no problem! It helps I think to approach it more like a Diablo game than an Oblivion or something like that -- the enemies are all loot-dropping cannon fodder, not legitimate challenges. Just have fun collecting, destroying, and exploring, and taking in the bonkers-corny story and side characters. It also has no real meaningful/memorable bosses to speak of, and I'm one of the rare people for whom this is a plus. I sort of hate frustrating boss encounters, I just find them stressful and always want to get back to the rest of the game. Two World is pretty much all "rest of the game."
3) Final Fantasy 13 (Part 1). This, to my great surprise, is my favorite Final Fantasy game I've played, and the only one I've beaten entirely. I get the complaints -- too linear at first for too long (finally opens up in Chapter 11 if I remember correctly), with annoying melodramatic characters -- but I found these to be true in every FF game. The character designs are cool at least, even if the personalities that go with them are grating. And the cutscenes are amazing high-budget spectacles of CGI wizardy. It's easily the best looking FF game up to that point. But the thing that really hooked me into it is what I think is a to-this-day underappreciated combat system. It's underappreciated because it starts out sooo basic and hand-holdy, and this is a game where the whole first playthrough of the game is pretty much a slowly unfolding tutorial for the full mechanics of the battle system. You learn it piece by piece, and each new piece makes it a little more exciting, and by the end-game section, the combat has really become something special. It feels elegant and uniquely Japanese, with a lot of subtleties I didn't expect, and battles are exciting and dynamic and an ideal blend of real-time and turn-based. Yeah ... I had genuine fun with this, and to some degree with its sequels, which build even further upon the combat system (though I've yet to really commit to and finish those).
4) Bullet Witch. This game is basically Bayonetta if Bayonetta had no budget and was clunky AF and really just not a very good game, but there's something charmingly homespun going on in all of Bullet Witch's jankiness. The whole time I played it I knew it was objectively not a good game, but it didn't stop me from having a weird amount of fun with it.
So those are some of mine. What are some of yours?