Based off the 2 and a half hours I was able to put into it this morning, I'm surprised by the low reviews. Funnily enough, the only reviews I even take the slightest bit of notice to are GameTrailers (they do the best video reviews) and they scored it a nice 8.6.
Reviewers are criticising it for being all graphics, 'no soul' (whatever that means?) - but to be honest the graphics aren't the best thing about it, for me the best thing was just how much FUN it is to race. If you're looking for a sim, yeah you're gonna be disappointed, but I wasn't.
To give people a rough idea of how long it will take to complete the main tour (career mode I guess) - each race has 3 stars you can obtain (for doing the challenges within the race like corner challenge, average speed, etc.) In total, there were around 200 or 250 stars to obtain, can't remember exactly, and by the end of me playing for just over 2 hours I had about 50 stars. I was able to do 95% of all the challenges of a race within my first attempt so far. The difficulty does increase as you go on, so I'm unsure as to whether I'll be able to keep that up.
I think the main deciding factor that people need to consider when thinking about buying the game is this - do you want to get involved in the online portion of the game? Not necessarily multiplayer races, but things like solo challenges, club challenges, etc. If you do, and you know people who will be playing this too, then it'll be worth every penny.
If you planned on buying this strictly to play offline only, with the career mode as your main objective, then you may feel short changed at £45 as it's no Gran Turismo. But at £30, IMO it's still worth a punt if you like racing games.
(not saying Driveclub is a 9 or 10, but not going to write it off based on critics alone)
