Overall, Red Dwarf: Back To Earth was a disappointment, albeit an enjoyable one; besides the blatant (and acknowledged) Blade Runner riffs, we'd seen all of it before, and done better. Fictional characters in the real world? Done. Outsiders commenting on our societal quirks? Done. Deus Ex Machina endings where the characters literally wake up and everything's back to normal? Done more than once on Red Dwarf itself, even. For a show where the characters kept telling themselves and us that they deserved to keep living and get new episodes, there was little proof that they could do anything but recreate the past.
(The plot, for those who want to know: the crew of the Red Dwarf discover an alien squid in their water tank. When they go to kill it, it attacks them, and they escape with a tentacle to investigate. Before they can do that, though, a new hologram appears, of the ship's science officer, who tells them that the squid can travel the multiverse, and using it, so can they. An experiment in doing so goes wrong, and the crew end up in the "real world," where they discover that they're only fictional characters in a TV show that only has a few episodes left. Eventually, they confront their creator, who they kill, before realizing that none of it is real at all, and that it's all a shared fantasy created for them by the squid. They wake up, older and wiser, and you're left wondering what the point was.)
That said, there really was a cosy nostalgic glow to seeing the cast back together and clearly having fun, even when the writing was letting them down (The first episode dragged terribly, and all the character interactions on the ship itself felt weirdly off, like everyone was trying to get back into shape - the show didn't have a laugh track, unlike earlier episodes, but it needed one, because the actors kept leaving the gaps in for the laughter to be inserted; it was only when the crew ended up on Earth that things picked up). Craig Charles' Lister is still, no matter how crappy the plot, an engaging hero and Chris Barrie's Rimmer still a great priggish foil, after all (Cat and Kryten both got unfairly stuck in the background a lot of the time, although Robert Llwyellen and Danny John-Jules did the best with what they had) and, more than anything else, it's their enthusiasm that made the whole thing worthwhile.
If you loved the original series, you'd probably find yourself liking this - it was, after all, just an overlong episode of the show. But if you'd been hoping for something more, something that'd be worth nine years of waiting, this wasn't it; in terms of reunions, it was that band you'd loved as a teenager getting back together for a greatest hits tour where they show that they can sound just like their old records, just without any of the passion that made you love them so much in the first place.