Tailgate up: Great chemistry; lots of action and visual gymnastics; not too heavy for the kids; and for nailing the mannerisms of Shatner, Nimoy, Kelly, Doohan, et al. Great character development of young Spock.
Tailgate down: Mecha-loud soundtrack (I felt like the "Is it live or is it Memorex?" dude); but another time travel, revenge script (sigh); the alternate reality pimpin' Spock; and lack of humanism that Roddenberry intended for the franchise.
Bottom line: Fun for adults and kids and just worth the price of admission ($26 per person - make Tommy Tow Truck so sad).