I've been for the past two years, an amazing experience and an absolute must for any motorsport enthusiast.
I've done both Dover-Calais and an overnight crossing from Portsmouth to St Malo. Cheapest is going via Calais, but is a long drive (on excellent roads I might add), the overnight crossing was a more relaxing trip. Bear in mind toll costs on the motorways. Traffic is not an issue.
We've stayed on a dedicated campsite a short way from the circuit, and I've appreciated the peace and quiet that brings. You'd struggle to get much rest on circuit, especially when the 911 RSRs are pounding round!
I've never felt like I've missed out with just an Enceinte General ticket, you're free to wander quite a long way. The Dunlop Curves as night falls is an absolute favourite spot, you really see the cars working hard through there. You can get to the start/finish straight for the start and finish.
One piece of advice, avoid the parade in Le Mans Town Centre, it's very...French. You won't miss much, spend it in one of the outside bars instead, or at some of the other events going on in the area.
You'll be certain to have a great time, nothing else like it!
Chris