I went there this weekend. It's impressive, even for me as a left handed bass player! It's a bit more of a "lifestyle" thingy, i.e. think of it as the Hard Rock Cafe but with guitars you won't buy instead of food you won't buy. People will go in there to gawp, as I did, at the guitars and it is worth a trip up that end of Oxford Street. On the ground floor it's all Gibson, tons of t shirts and hats etc. but get this, £69 for a Gibson t shirt(!!!). Or you can go downstairs to the Epiphone and Kramer area and pay half that for a t shirt that's just as good, I'm not joking.
In the downstairs bit there's a stage set up where I guess they plan to have some minor performances and there's Mesa Boogie amps everywhere for people to try guitars and basses. Lefties are surprisingly well catered for, as are bassists. No left handed Jack Casady basses though, sadly. In fact, no lefty basses at all, but that didn't stop me having a go on an Epiphone Newport.
Everything is at full RRP which is a bit silly as I can't imagine they provide a set up like the established decent guitar shops do. Also, there are security staff everywhere, as is understandable when there's probably well over £1m (at full RRP) worth of guitars in a very, very busy shop. They're also really bl00dy annoying, won't leave you alone for a second asking if everything is ok or if you like a guitar, but the staff that know the guitars etc are a lot better to be fair.
I didn't think I was a Gibson person until I was in the shop and thought out of my five basses and one electric guitar I've got one Epiphone bass, one Kramer bass and an Epiphone electric. So I guess I am a "Gibson guy".
Overall, whether you like Gibson or not, it's worth a visit.