I wonder if the enjoyment in your playtest games comes primarily from the rules themselves, or if it is the result of your group's playstyle? That is, do you think you would be having just as much fun with a different system?
That is a fine, fine question.
I'm kind of a system whore. In the past year I've played D&D Next, 4e D&D, 3e D&D, Old School Hack, Eclipse Phase, Savage Worlds, Ashen Stars, Night's Black Agents, Fiasco, Time & Temp, Inspectres, Danger Patrol!, Paranoia, Don't Rest Your Head, Marvel Superheroes, Mutants & Masterminds (both 2e and 3e), Leverage, Dread, Call of Cthulhu, Og!, RISUS, and a few games I'm forgetting. That gives me a decent baseline for comparing rules vs players vs scenario.
In addition, my playtest group is large - about 12 people, with available folks swapping in and out depending on who's available on a playtest night. It's not the usual group of players, so there's less of a "yay, the gang's all here!" feel to it.
I believe that my satisfaction (or dissatisfaction) with aspects of the rules is independent of whom I'm playing with. The opinion I'm expressing here is based on system mechanics and play, not roleplaying or friendships. I'll be able to confirm or recant this; I'm running a playtest game at PAX East for strangers, so we'll see if my opinion remains the same.
Having said that, I'm going to politely back out of this thread. It's a topic I want to talk about, which probably means I should give it a wide berth until NDAs are relaxed.