I cannot imagine how you can say the gameplay mechanics are even similar in the two games. They are both turn-based, but thats pretty much where the similarities end. The combat system is different, the leveling system is completely different, and the equipment system is only vaguely similar. The fact that combat is done in set rounds rather than based on speed of characters to gain actions faster than your opponent is a huge difference in and of itself. The ring system is also a major change in how the game functions and that is just addressing part of what makes the combat system so different.

 FFX is in no way better than LO from what I have played. Unless the fourth disc suddenly turns around and starts sucking on me then the game is just hands down better. The characters are more interesting, although painfully under-developed. There are definately some issues with the game that stick out like a sore thumb at times (why are the immortal characters hands down better than the mortal characters?) but it never detracts from it too much. The writing is decent and the story is pretty ok. I would say if you like the genre and own a 360 you should buy the game.

FFX was the better game overall because:

1.The Seymour in FFX was a way more complex villian than Gongora

2.There are some technical issues in LO than FFX didn't have

3.LO's story was actually pretty generic(character interactions=/=story)

LO's writing and VA were pretty decent though.

EDIT:If anyone wants to explain to him that while LO is great, the reason why FFX comes out as the better game overall

 I haven't quite gotten to the point where they explain why Gongora is doing what he is, but there are a number of good ways it could resolve. At any rate, Seymour was an annoying and mediocre villain at best. His motivations were pretty straight sorward, and there was next to no depth to the character. He really was one of the low points in FFX that I do my best to forget when remembering it.

 And what technical issues does LO really suffer from? There is the excessive load times and thats about it. Other than that the game seems to work flawlessly for me. The story is generic, but then so was FFXs. 99% of JRPGs have generic stories. It is just the curse of the genre. In the end I credit the game with better writing with the better story as a result.

Actually, Gongora is why more straightforward than Seymour. Seymour is not actually "evil" for one. Gongora's motivation is the most cliched motivation ever used in an RPG. Seymour's motivation isn't. Gongora is revealed to be the villian early on in LO whereas Seymour is not revealed to be the main villian in FFX until like 20 hours in. Yes, FFX's story uses chiches but even the good JRPG stories use a few cliches, it's unavoidable. Why do people pretend that LO's story is the best thing ever in a video game when they probably know it's generic? FYI, character interactions(one of the strong points of LO and FFX) should not be confused for story.

EDIT:LO's story does have its moments

Gongaro gives off the creepy vibe from the moment you see him, whereas Seemour does seem to have more depth to him, though Sin is the real enemy, and I really did like all that stuff, and Auron is just plain awesome. My main problem with Lost Odyssey is that I was bored for like 10 hours of it, though it has really taken off now.

And with immortals being infinitely better than mortals, it is mostly true, though you need to keep on levelling the mortals to give the immortals all their abilites, so the best thing to do is probably just to leave them out for the boss battles, and the later mortals definitely add more.

I just found the battle system in Final Fantasy X better, more immediate, and I prefered the setting. For much of the time in LO you do just seem to be wondering around without much reason, though as I have said, disc 3 is miles better than the previous discs

There's just something FFX has that LO doesn't.  Don't know what though

 You just rotate the one token mortal in the group to get their abilities. The fact that you can't grind past a certain level makes it fairly easy to keep them maxxed out and then just siphon their abilities off as needed.

 I find it odd how LO's combat system manages to be slower while still being more involved. It is definatly a few notches slower than your typical FF, but that is a side effect of the style of turn-based combat they used (for the curious it is like Legend of Legaia, Final Fantasy 1-3, or your typical SRPG but without the need to focus on character movement). The ring system manages to keep you engaged in the combat most of the time at least.

 As an odd counter to your experience I really loved the early bits of Lost Odyssey, but have gotten bored on disc 3. There is a specific complaint I have about it that might be pulling the whole experience down though. The spoiler free version (or close to it) is the part after the train annoys the crap out of me. Although given that you found disc 3 miles better while I found it way worse it is probably just a matter of us enjoying different parts of the story more. Still disc 3 is plenty of fun and well worth playing through.

 @Riachu

 I am not trying to say Lost Odyssey's story is the best ever. It is an above average JRPG story in my opinion. Of course I accept that every video game story will likely be cliche at best and judge them best on how well written it comes out. I think we can both agree that the writing in Lost Odyssey is better written than Final Fantasy X. The only major problem I had with Final Fantasy X was the story was pretty good up until the second fight with Seymour where it died a horribly tragic death.

@ gnizmo, I am only midway through the 3rd disc

SPOILERS AHEAD

I am getting a bit tired of having the split party, and I would like it if I could finally play as Kaim again... I am tired of having Mack as my only melee fighter, especially after I have finished the good part with Tolten, Sed and Seth

That is the exact same problem I have with the third disc. It doesn't resolve itself until the very end of the disc.

Thousand Year Stories > Any FF story ever told (except maybe VI)