The leftmost girl (no, not Luke, the red-haired person) is named Tear. She's basically a guide for Luke throughout most of the beginning of the game. She's also a spy that spies on people, I'm sure you have experience with that, Xyro, on BD. =P (No, really, she actually is a spy sent to assassinate Luke's sword instructor, no joke)
There are about 30 Tales games out right now, most of which were released in Japan only.
Of these, several are incoming re-releases (ports, enhanced ports, actual remakes, etc), spin-offs (around 15-20) and around 12 mainstream games (you can compare this to the main Final Fantasy branch of games).
The spin-off series are basically non-canon (Radiant Mythology series, Nakiri Dungeon series, etc) and are basically "What If?" scenarios that really are made just for the fans' pleasure.
The series is split into 2 sides, the Mothership titles and the Escort titles. Titles such as Destiny, Eternia, Rebirth, Symphonia, Abyss, Innocence, Vesperia, Hearts, Graces and Xillia are considered Mothership (the main games of the "main" series) while games such as Tempest and the Nakiri Dungeon/Radiant Mythology series (note that RM is basically a continuation of ND due to the development of stronger handheld systems; these 2 series were basically made with the purpose in mind that they are "on-the-go" Tales games the player can enjoy) are considered Escort. Incoming Mothership games include Tales of Graces f for the PS3 in about a month and a half for North America and the re-release of Tales of the Abyss for the 3DS.
I've played most of the games in this series, and I've found that the most exhilarating game I've played thus far would have to be a tie between Graces and Destiny 2 (not to be confused with Destiny II, the released version of Eternia in the US when it was released for the PSone in 2000).
Destiny 2 and Graces introduced the concept of aerial special attacks that can be used after standard combos and artes, depending on the character. Emil from Tales of Symphonia: Dawn of the New World, shares this trait. Couple that with the fast paced action that is notable for the series as well as the new replacement for the TP system (the TP system is replaced instead with another type of point system: it is restored over time when you rest and deal out damage or take damage. This means that one must conserve these points as much as possible because they are easily used up in one combo in the latter parts of both games).
The worst game in the series for me would have to be Tales of the Tempest for the DS. Unlike Tales of Innocence which was also released for the DS later (and will be re-released as a remake with new additions much like Graces f for the PS Vita), this had a new battle system that the players play on a 3 separate lines as opposed to the one line most people are familiar with (coupled with Abyss' addition of Free Movement in the background and foreground). The problem with this is that if one monster is taking your attention, it is not possible for someone else to come help you as easily as it is in other main games, because you must physically jump to the next line and risk the other monsters ganging up on the other party member. Note that this game only allowed 3 party members (Innocence, as well) as opposed to the standard 4. Also, this means that skills (or Abyss's rendition, artes) cannot attack monsters in a group that have AoE effects as easily because they are separated. Plus, the story was just stupid and the voice acting wasn't very good. The visuals were good for a DS game, but that's all I can say for that game that's actually positive.
Ranking Tales of the Abyss for me would probably be an 8/10. Newer games in the Mothership series always base themselves on what Abyss established (the ease of the usage of Mystic Artes, artes changing form, 3D movement, "AD Skills" that aren't as limiting when compared to Symphonia [even DotNW copies Abyss's system of "AD Skills"; they add a point system to make it balanced, though, as does Vesperia). To me, Abyss was the start of something great, and the voice actors in Abyss are some of the most famous ones now compared to then (Johnny Yong Bosch, Yuri Lowenthal, Laura Bailey, etc. These 3 are almost always together in games they voice for, more often-than-not the former and the latter [e.g. Laura voices Chun-Li and Johnny voices Zero in UMvC3; Yuri voices an NPC as does Johnny and Laura voices Catherine in Catherine; Laura voices Marta and Johnny voices Emil in DotNW).
I will be purchasing this game, regardless of the amount of playthroughs I've done for the PS2 release version. I'll take any excuse to play this game again, especially on-the-go. For anyone who hasn't actually played the series at all, this is a good place to start.