I always have a little trouble initially with alien cast members (I didn't like Spock when I first saw him), and Phlox reminded me too much of Neelix with his makeup and constant merriment. Though a continually cranky alien might be hard to take, too. T'Pol might fit the cranky mode though.
Trip's accent didn't bother me too much, as I knew people who talked like that back in the Ozarks (which Trinneer apparently based it on). It was a risky choice, because Trip could have easily turned into a good ol' boy redneck ala Dukes of Hazzard.
And poor Travis winds up with the short stick. We learn he grew up on a freighter, but not much is made of it afterwards. And after establishing he's an outdoors type, later references to that have him get injured while rock climbing or he's the first crewman to be incapacitated by the threat-of-the-week.
But the actors all seemed to gel with their characters and relationships fairly quickly. Scene chemistry was pretty good all around, just about any two of the actors could be put in a room together and create something interesting.