I think in the evolution of this relatively young platform every manufacturer has had it's share of missteps. Samsung's are naturally the only ones people here care about, and it's well justified.
I've barely had this Vibrant half a day, so it's not like I have any long term anecdotal evidence or anything. It's certainly not flawless. But Samsung is putting a lot of their eggs in one basket with the Galaxy S line, launching phones on multiple carriers around the world. Given that I'd say Samsung has a lot at stake getting this one right, and I'd add they seem to have hit on nearly every mark with this one.
It's media playback capabilities are arguably superior to......everything. The included audio player is not only the best I've ever seen on Android, it's a fair sight better than the one in iOS3 and iOS4. The video player has played most of the videos I've tossed at it without transcoding (my MKV collection notwithstanding, but RockPlayer takes care of those). The dialer and contacts apps are slick and offer a great deal of customization. And, it reliably makes phone calls without FC'ing or locking up, something my Behold II constantly had issues with even after I had all the other nagging problems put to bed.
It's too early to say for certain, but given what Samsung has at stake with this platform, I think it's going to be a huge success. And before I turn this into a full review I'm going to STFU!