Calling any keen cyclists

Hello folks

I have been on a few bike rides recently after many years of no cycling.  I've enjoyed it so much, and surprised myself by keeping going up all the hills, that I've decided to purchase a bike.  Luckily I can get one with the 'cycle to work' scheme.

So, I've been researching and the obvious choice from the word go was a Hybrid.  I'll be doing road rides and some light offroading, mostly in rural and hilly areas.  I was going to get a Hybrid with 29" or 700 wheels, geared up more for a bit of off roading, rather than a 'city'/'commuter'/'road' type.

However, I then came across cyclo cross bikes... I think I would have way more fun on one of these.. cover more ground on road rides, balst up the hills more easily.. but how at what point will 'rough' terrain become too rough?  Gravel and mud, no problem... but forest tracks with tree roots?  I'm not planning on the downhill trails or anything, but want a versatile bike...

Is anyone familiar with cyclo cross bikes, and what do you reckon?

Thanks!