Here's my experience of riding the R1200GS (the later, water-cooled version).
I'd been riding for just 3 years, on a CB500 with forty something bhp. I'm 5' 7" and can bench press 30kg on a good day. If it wasn't too big for me, it isn't for you.
The bike is a complete blast; it's a great bike, super-comfortable for all-day riding, it eats motorways effortlessly, loves twisty roads, and will even off road when your sat nav tells you the quickest way to the YHA is over a mile of muddy track. It's once of the best all-round bikes out there.
A couple of small negatives:
wide bars mean it's harder to filter: fine on a motorway, but I used to get stuck in London traffic, while the scooter boys were whisking around me
lots of torque (which is nice) mean it revs low, and you don't get the wild hooligan feel of a inline four nearing the red line.
... but nothing there to put someone off.