If you liked Symphonia:
Tales of the Abyss -- I've seen a number of people who didn't like this one because of its story, but the story is actually one of the things I liked the most about it. It's got, in my opinion, a cast of interesting characters, and though the main character is pretty annoying, it works into the story pretty well, and starts to make more sense later on. I want to emphasize here that the MC's character development is crucial to the story. The battle system is pretty much an improved version of Symphonia's, and also introduced the free-run aspect, which allows you to move in any direction if needed, as opposed to the linear movement in Symphonia. I also love the Field of Fonons system, which allows you to use different (usually improved) versions of moves in battle. I think this was also the first game to start using full-sized character models as opposed to the chibi-like models in previous games. It's also got my favorite soundtrack of the games. I personally consider this one of the best Tales of games, and it shuffles in and out of my #1 spot.
Tales of Vesperia -- This one's got a great cast of characters like Abyss, and a pretty good story as well. I really liked the relationship between the main heroes Yuri and Estelle. It also looks really good, having returned to a cel-shaded style, and has a lot of interesting locations. The battle system is like a slightly improved version of Abyss's, although there aren't any Field of Fonons... ;'( The game's also got a pretty good soundtrack. Though I can't really think of anything to say about this game that makes it amazing, I can't think of anything bad either. Overall, Vesperia is just a really good, definitive Tales of experience. It's hard not to love it!
Tales of Graces f -- Like Abyss, although even more-so, this one is often criticized for its story and characters. Unlike Abyss, I can sort of see why. Sometimes the characters are a bit annoying, in their actions and general personalities. But I didn't think it was that awful. A bit cliche, yeah, and maybe not amazing, but it had its moments, and overall I liked it. The battle system though, is one of the best we've had in a Tales of game so far. It's a lot quicker than the previous games, and does away with TP in favor of CC points to perform your combos. At first, I didn't like that, but it actually worked out quite well, and allowed me to feel less limited when performing combos. It's not my favorite battle system, but it's definitely one of the best, and if the gameplay itself is one of the reasons you enjoy Tales of games, you'd probably like this one just for that.
Tales of Xillia -- One of the best Tales of experiences I've had, up there with how much I enjoyed Abyss. The characters are all generally likeable and have some of my favorite character designs, and the story was fairly enjoyable, much more so than Graces f. The setting itself is really nice looking, with some very interesting locales that vary from anything we've seen in previous Tales of games in both style and vastness. It's also the first game to allow you to fully control the camera around you outside of battle. The battle system is very similar to Vesperia, except a bit faster, along with a linked-combat system, where you can link up to another party member and perform combos together, which works pretty well. One thing I didn't really like about Xillia though was the lack of interesting dungeons. The fields outside of towns felt like bland, generic landscapes with monsters and treasure randomly sorted throughout them. The "dungeons" that did exist didn't feel very interactive, and I felt like there was a distinct lack of puzzles in the game. Regardless, I really enjoyed Tales of Xillia and would definitely recommend it as one of the best Tales of games in recent years.
Tales of Xillia 2 -- I've got to be honest with you, I'm skeptical about recommending this one. A lot of people seem to like it, and the general consensus seems to be that it's improved over the first Xillia. But I actually don't agree with that. I liked the first Xillia better. The new characters in this one are great, in both design and personality, and I really liked the personal relationships between all of them. The returning characters were also as likeable in design and personality as they were in the first. However, and this may be borderline spoiler material (though I'll try to word it ambiguously), I felt like the Xillia 1 cast were more like observers than part of the actual story in Xillia 2. The game tried to include them and make them feel like their existence and past experiences from Xillia 1 were directly relevant to Xillia 2, but I wasn't really convinced. At the end of it all, I felt the inclusion of Xillia 1's cast was more of an obligation than anything, and the over-abundance of main characters made it difficult to care for each one individually, though I still ended up liking the new characters quite a bit. Also, considering the game is a sequel, I expected to revisit some of the past locations from Xillia 1, but the re-used assets highly surpassed the new ones, which was kind of disappointing. There was maybe a handful of new cities and locations. Although, I will say that I found the design of some of the new locations to be very interesting, particularly the modern or futuristic-ally inspired ones. As for the story itself, I was also left feeling a bit disappointed. I've already touched on how I felt the returning Xillia characters didn't tie into the story very well, despite the game's efforts to do so. Though the new characters themselves were interesting, and I really liked the relationships between them and how they applied to the story, towards the end, I started feeling like things weren't coming together very well. I won't share my detailed opinion on the ending, but it's easy to infer how I felt about it. The MC Ludger's lack of a voice only ever worked against the game, though I have yet to play through it again with his voice on to see if that makes any difference, though it likely won't since the dialogue itself isn't going to change just because he's voiced at certain parts. Anyways, despite what I didn't like about the game, it wasn't all bad. The battle system was essentially the same as Xillia 1's, with the exception of Ludger and his abilities. He's able to use "special powerz" to change weapons in battle, as well as change into a special form that allows you to use some really neat moves. He's very versatile, and likely has the more moves at his disposable than any of the previous Tales of MCs ever! Also, if you really liked Xillia 1's characters, you'll probably love seeing them again in Xillia 2. Each character has their own short side-story, which I thought was pretty fun. And the ability to make "choices" throughout the story was pretty neat, even if most of the effects caused by these choices were incidental. It was a fun game, but didn't live up to my experience with Xillia 1.
And... that's that. I think I typed too much with that last one.