My sentiments exactly
To be honest, the engines were designed for smoothness and economy, not out and out power. Bear in mind the 'little' C20XE of Astra GTE / Cav GSi fame put out 150bhp, so compared with the X25XE there's a whole 500cc more but only 17bhp difference? Sounds like the V6 is 'rubbish', but of course one is aimed at pushing the power envelope, the other for relaxed cruising.
Mind, the power is accessible, if you go down the much-done G-Cam mod (3.0 cams in a 2.5 for those not aware) which takes the engine to a theoretical 195bhp, which is much more like it. 
But also has 30 Nm more, acheved at lower revs. Not to mention much smother torque curve. GM V6 wiht multirams have a very nice trothle response compared to many other engines of comparable size and power, especially on low revs. This really makes it pleasant to drive. Also, IMO, this smoothnes 'erases' the feel of acceleration - they have more grunt than you feel. Multi-ram is really a great thing for a daily driver.