I have no idea what happened here based on everyones posts... but i think this is an interesting topic.
i think the key to 3rd party success has been down to multiple factors. i think this is evident in terms of the new IPs this gen, that have had to compete with well established brands, yet some 3rd party games (Assassin's Creed) which are relatviely new have been able to go toe to toe with the annual Call of Duty release.
the first thing has to be when it came out, the reason i think Mass Effect, Assassin's Creed, and others new IPs are so popular for the moment is because they came out so early in the gen. because of their originality and the the exposure they got when they came into the market we were very early in the gen. they didnt even get great reviews. yet because they established the brand so early in the gen, with relatively little competition their sequels have been very successful.
if we look at other games this gen, say Castlevania LOS, or Enslaved, we can see they were recieved very well, yet have not performed commerically well. i think this is because they have come out relatively late in the gen. while they are competing with Assasssin's Creed, or other new IPs, they cant compete with the fanbase those franchises built up from their inital installments. despite how mediocure those predecessors may have been.
i think the 3rd party market is over saturated, and the main way a game can be successful is by internet recognition. Demon's Souls comes to mind, the game got stellar reviews and i think the reason its done so well is because it was a PS3 exclusive. the internet gave this game massive exposure. and now Dark Souls is multiplatfom. the game is a guarrantted success because its already selling to a pre-established market from Demon's Souls.
theres only a handful of new IPs i would say have done well, based on timing etc. but the reviews make or break a game these days. the difference between 8.5 or 9 from IGN could determine a few hundred thousand copies sold. sadly it has meant many amazing gaming experiences, like Castlevania or Enslaved get lost in translation. and in this type of gaming climate a first party exclusive can sometimes guarrante success. i mentioned Demon's Souls, but another example is say Heavy Rain, which was doomed to fail. however a different set of factors come into play with the Wii, as i think we will find out from Xenoblade.
