I'll chime in here...
I was one of the original Arena Rex
KS backers and absolutely I love it. The miniatures are what drew me in as well, but I really enjoy the gameplay as well - I've never not had a blast playing.
IMO it's streamlined, dynamic, fun, and easy to learn - the rules are straightforward, the damage tree for each character is a unique take on combat effects and makes for some very cinematic action, and the fatigue mechanic calls for thoughtful management throughout the game. During the
KS the Red Republic Games guys billed it as "simple to learn, difficult to master" and I'd largely agree with that.
Here is a quasi-battle report I did for a small game - it gives an overview of how the game works and I think it shows off what sets it apart from other games.
Also,
here is a link to the spot in my painting blog where I start on my Arena Rex stuff - building an arena, assembling hazards, painting models, etc.
Finally,
this is a link to the second iteration of the ruleset. They've since changed slightly, but it'll give you an idea of how it plays.
Let me know if you've got any more specific questions.