The cpc6128 is one of my personal favourites and I'm very pleased with my one.
I bought her a year ago, but she was languishing in my loft until January when I started to work on her properly. I installed my HXC internally and have further plans for that, but it was a disappointment to discover that she wouldn't run a lot of software without crashing randomly.
I suspected a RAM failure and set out looking for replacements. Luckily I have a dead Spectrum +2a and the chips are the same so I spent an evening carefully desoldering all the chips, soldering in some new sockets and then fitting the replacements.
Once completed, she worked perfectly and it was great to see the Batman demo for the first time on original hardware.
Protek has already mentioned the R-Type demo which is graphically a massive improvement, but I found it much less forgiving than a lot of other versions and consequently it takes the edge off slightly when you find it nigh on impossible to get to the end of the first stage! Still, had it been released like that in the day, it would have absolutely blown the opposition to tatters.
Another massive improvement is the Bubble Bobble remake. The original was utterly diabolical, terrible graphics, odd colours, poor gameplay and silent! The remake is an radical improvement in all these areas and much closer to the original arcade (although still not perfect of course, I reserve that for the NES version). Thankfully the revised version now includes the famous music.
Of course there are new exclusives like Star Sabre which is also monstrously difficult, but a smooth and fast scrolling schmup. Also, the highly regarded ChaseHQ which again kicks all other conversions from the time firmly in the crotch and runs away with their lunch money. Unlike all it's competitors, the 128 version includes digitized speech!
I also have a place in my heart for Cybernoid. At GEEK2012 we sat the CPC and Spectrum +2 next to each other and played this game, the Amstrad version is just so much better in almost every single sense. The only real game I was disappointed with was Rodland (pictured above) It looks awesome but the gameplay is just a bit slow. I guess I am spoiled by the C64 version, which is quite frankly brilliant.
I can't recommend a CPC highly enough, when combined with an HXC (which was developed with CPCs in mind) it is a brilliant 8 bit gaming machine. It's just a shame that it developed such a poor reputation with some lazy spectrum ports when it was a far more capable piece of kit.
No collection is complete without one.