I have played off and on for a couple years.
I have run most of the low level content, and have even played some of the end game content (they moved the end game out recently and I have not hit the new end game content).
Unlike most MMOs, you are limited to only a handful of powers being usable at any time.
You do have an NPC companion you can level and who assists you in combat. You can only have one active at a time, plus a few that are offering some stat boost, but not out on the field. You can collect a lot more of them than you have active plus semi active.
There is a profession system that is interesting, you collect minions and send them off to do jobs. The jobs usually take hours, so I tend to send mine off once a day on really long missions and log out each day.
The story line is decent, no SWTOR, but at least as good as the WoW stories.
The graphics engine is newer than WoW's so the graphics are decent, but it is not constantly refreshed like say EVE Online so it is aging.
The F2P is tolerable, most of what you would buy is cosmetic or secondary (like faster mounts or more bag space).
Overall I give it a B-