I actually consider the West Highland Way to be one of the most enjoyable rides I've done, which just shows the extent to which different people like different things.
As said before, if you are looking maximum technical trail per mile you'd be better fed elsewhere. But unless you're only ever going to ride Scotland once why rule it out?
For me, I like a ride to be as much about the 'experience' than the riding itself – including amongst other things the scenery, the company, the drinks after the ride, the discussion after returning home. In terms of achievement a multi-day ride from A-B beats riding all day in a circle hands down every time.
The scenery on the way is definitely amongst the best I've experienced in Scotland. And some of the riding is pretty good too – Conic Hill is good for a quick bit of fun; there are a lot of small rooty sections between Balmaha and Rowardennan; The descent to Kinlochleven after the Devil's Staircase is often talked about but I also enjoyed the lead up to it after the Kingshouse Hotel, and the final bit out of Rannoch moor.
In terms of gates there are quite a few between Milngavie and Drymen, but they don't seem to bother me. Mostly they're on sections of a perfectly flat well surfaced old railway path so I don't find they're interrupting anything that'd otherwise be fun.