I'm going to admit, I think the only flaw Xenoblade has is that its side missions are pretty generic. Lots of find X amount of Y, or go kill this. (At least at this point in the game)
Its still pretty addictive though. I've just spent about 2 hours just doing sidequests (because I felt like it).
And I really love killing those special monsters. Especially going back and getting revenge on the hard ones you had to avoid earlier on in the game! XD
(I've seen lvl 70 monsters! One was in a lake and I was like "huh why is my spidey sense going off" and then I see this lvl 70 fish and I was like "OMFG! RUUUUUUNNNNN!!!!!" (Game doesn't really penalise for death but it was inconvenient at the time))
The main story is great though, I'll give it that. And I have to say again how I love how rewarding the battle and collecting and creation systems are. Unlike say FFXIII, it really lets you get tucked in on the game. I've already played it for 10 hours and while in FFXIII I had to quit at this point, in this game I'm like "MORE! MORE! MORE!

".
Probably at least going to spend about 20-25 hours on this game minimum, probably even go beyond the 40, which is really rare for me, (I get distracted from RPGs very easily).
Haven't even wanted to play Pandora's Tower yet or even go back to Metroid Prime or some other Gamecube games, (except Melee. Having a little go on that since my Brawl has vanished sadly..

), or even the Xbox 360!