I played DS:E, bought at full price, and I enjoyed it very much. Co-op mode with my brother, no bugs, and we even stuck around to watch the motion comics we'd unlocked by beating the game! I don't think it has serious flaws as a rail shooter, we found it engaging, fast-paced, and VERY interesting to follow.
That said, I have to admit that I would rate Resident Evil: Darkside Chronicles as the better "game." Dead Space Extraction was newer, more unique, and more fresh, but in terms of just gameplay it didn't involve the player with "game" elements like purchasing level upgrades or looking for secrets.
Still, my brother and I couldn't put down DS:E once we started playing it. I really am saddened to hear that a lot of people were disappointed in it. I happen to LOVE Rail Shooters, and the Wii's been very good to me in this regard. I'm still waiting for a port of Area 51, but until then I'll be replaying both games. A friend just bought his own copy of RE:DC, and I'll be bringing my own copy of DS:E for him to try out.