The only bad HK firearms I knew were the first generation of USP pistols. We had six of them at the rental range I worked at, and a year later, five were back at the factory for repair. The Tucson Police Department used them, and ever week the Armorer would come over with a box full of USPs to test fire after repair. TPD finally ditched the USP and went with Glock. I was working there when one officer stopped by to crank off a few round from his duty USP in uniform - it went BANG every other time...and he left pretty shaken up, presumably to go get a new gun.
We had a P-7M8 that worked like a charm, even being old and very beat up. We had a couple of the uberexpensive G-36 wann-bes in 45ACP...can't remember the model number, but one actually made it on the rental range for a short time until someone waved a LOT of filthy lucre under the bosses nose. Very nice little carbine. I haven't had a chance to try much else from them except for, of course, MP-5s - we had an HK rep who would drag around a cart load of MP-5s to show off. Also had the chance to shoot an FBI issue MP5/10, the MP5 in the a sensible subgun caliber, 10mm. FUN!!! Only 2 round burst, but FUN and accurate. Too bad I'll never get to legally own one.
That's it, hope that was what you were looking for.