There have been plenty of reviews written about the VP9, I've read them all before I decided to pick one up myself a few months ago. However, already owning the P30 made the decision easy for me, as I've become attached to it - outstanding all around.
The VP9 is more than a striker fired P30, in more than just technical terms. Sure, HK used multiple P30 parts to drive down the cost of VP9 production, but there are some very important features that set it apart. Weight, the VP9 has a little more heft, not much but holding both you can tell for sure. Barrel length is increased with the VP9, putting it somewhat between the P30 and P30L. Grip is pretty much the same, which I think HK fans and prospective buyers will appreciate the carry-over. The trigger is probably the best feature, it is light, it is crisp, and it is great for quick and controlled shots on target. I've been told it was a feature that HK dropped in from a Walther platform - if so, great move. Other than that, the muzzle end of the slide and frame are squared in comparison to the P30 which has an angled end the handgun.
Magazines - a blessing or a curse? Because the VP9 shares 10/15rd magazines with the P30/P30L, it saves HK from having to produce another magazine design. Now, because the VP9 is very popular and the P30 has been a steady player over time, getting magazines can be a task. Availability varies but for the most part they maintain the $60-$70 price point (which is high, but HK does that because there are no real players in the aftermarket game for these platforms)
The VP9 fires absolutely smooth, the HK proprietary recoil buffer does its job, and the grip allows the shooter to be comfortable - unlike the horrible grips on many other 9mm platforms on the market. Trigger pull is crisp, consistent, and fairly light in my opinion. I say that with a caveat, after shooting the hammer fired P30, which because of the double action - feels heavy. If I needed to pull a handgun and engage quickly, I know the VP9 would be an ideal choice. It shoots like an HK, I say that as an honest "fanboy" because I've had the displeasure of shooting some other makes and I appreciate what they build. I respect the research and what they offer to the civilian market, it is a better handgun overall. I have yet to run the VP9 and the P30 in a serious head-to-head battle of what shoots better...but that day is coming soon. Breakdown and cleaning is easy, besides the striker mechanism, it is practically the P30...simple design, robust and well done.
A notable Glock spokesperson has stated something along the lines of "HK has built a striker fired 9mm handgun in one try that Glock has been working 30 years to perfect". The fact that Glock has yet to hit the standard of HK in terms of reliability, or comfort is telling. Glock fans will offer up many arguments, but in the end - Glock is not HK in terms of product. Does it work? yes, and for the most part very well. Would I put the VP9 up against any Glock 9mm...ABSOLUTELY.