Abyss is pretty neat, just don't expect other games to be quite as broken :V
Also pretty much all the games have standalone stories so you don't have to play them in order or anything.
As for Graces, I personally prefer its battle system over games like Abyss or Vesperia because:
-Fast movement + free run tends to make dodging things like spells easier than it should be. Especially Abyss, once you get Dash and/or Glory, there's really no reason for you to get hit by anything, which kinda makes it boring in a way. In Graces you can still dodge a lot of things with the movement options you have, but sometimes you'll be forced into a situation where you have to block or parry. For example, at the end of a combo when most of your CC is used up, and you can't run fast enough to avoid the counter attack or another enemy's attack.
-Parries own. Parries are basically my favourite part of this game. It's basically a risk/reward system: block an attack and possibly get guard broken, or parry and possibly negate almost all damage(and gain bonus CC) or eat damage if you mess up. (Also "option selects" with parry since you have to hold block to parry :V) Meanwhile, Abyss and Vesperia don't really have the same sort of thing, since free run makes you almost untouchable, and even if you blocked, I don't remember ever being guard crushed in those games.
-With the movement options you have, it's still possible to play runaway, but CC makes it harder to run for long. At some point, you will probably have to block and/or parry to regenerate your CC. As for Abyss/Vesperia: infinite free run and backsteps that cancel into themselves forever say hi
-CC in this game is better than ToDr, since it increases as you perform as opposed to just increasing by one each time you use more than 1 cc until it hits the cap.
-Being able to block magic means not getting hit by "unblockables" because an enemy casted a spell, but you're too busy blocking a melee attack from another enemy to magic block the spell. (To be fair, this probably doesn't happen very often anyway)
-Other neat little things like "charging" block to change your next attack's properties, or sheathing Asbel's sword at the end of long combos to regenerate health.
Basically, I probably like it because it's a lot like a fighting game! :>
It's by no means a perfect system though. There are some things I kinda don't like about it, like not knowing when you'll be guard crushed(guard gauge???). I also miss things like push blocking/advancing guard/whatever block+forward is, or the "parries" in ToDr you could do by tapping block before an attack.
