Hm, I have a few ideas for recommendations for you... First, let's start with the ones you're thinking about.
Dragon Quest 5... I've played 9 and 6 and have enjoyed both of them, so I'd assume 5 is as fun as them.
Metal Gear Solid 4... Heard good things about it, but never played it.
Super Mario Galaxy 2... Good game, but in my opinion the reviewers idolized it a tad too much.
As for my suggestions, well, let's give a few per platform.
Wii: Donkey Kong Country Returns is a ton of fun (
http://www.belltreeforums.com/entry.php?187-A-Corny-Review-1.-Donkey-Kong-Country-Returns! here's my review on it, by the way) and perhaps Goldeneye 007 if you're looking for a FPS.
Xbox: 360 or regular? If 360, I'd say Assassin's Creed 2 (old, but fun!) and Halo Reach
Playstation 3: Soul Calibur 4 and MAG are very good games!
PSP: Prinny: Can I Really Be the Hero is a fun game (I'd buy it on the shop, hard to find in stores) and perhaps Half Minute Hero (though I'm barely on my PSP)
DS: Dragon Quest is a good idea. Also, Pokemon Black/White coming out on Sunday (not sure if you're into that kind of thing)
PC: I'd really recommend Minecraft if you're looking for customization!
I dunno if you have any of these games, but yeah. Let me know if you have any questions or whatnot!