Do you want me to give a general statement or on each game? If the latter I'll give some thoughts on each entry I've played and a cliff's notes score.
Tales of Phantasia SNES - I enjoyed it but only because I was new to the Tales series. 5/10
Tales of Phantasia GBA - Hated it
Tales of Phantasia PSX - Wish they had translated it. 7/10
Tales of Destiny - Liked it enough to play all the way through. 7/10
Tales of Eternia - This was where I really started liking the series. 8/10
Tales of Destiny 2 - The battle system was a little broken, and the story was complete shit, but it was a fun diversion. 7/10
Tales of Symphonia - I still say it's the best game on GameCube
Tales of Rebirth - An acquired taste, the battle system is kinda weird at the beginning but I loved the game. 9/10
Tales of Legendia - They went and took a step back, but it was still okay.
Tales of the Abyss - I used to consider Symphonia the pinnacle of the series, but you can see my review above.
As a general sense, I think you could consider me a fan of the series even though my scores for each game probably don't reflect that - I tend to ignore problems in the games if they're small, but I do have my limits (Phantasia GBA sucked all around and Legendia's battle mechanics and graphics were atrocious). I can say without exaggeration that Abyss is probably the pinnacle of the series; there's no downgrade from previous entries, and the battle system isn't some weird funky thing you have to get used to like Rebirth. Think of the battle system as similar to Symphonia's except much more refined.