Well I didn't come from the HD, but I did come from the Galaxy S3 which is very similar.
The S3 was an awesome phone and what is even better is that the bootloader is unlocked (I was on verizon) and so all sorts of terrific development was already available. I had it for two months before looking at the Razr M. The specs pretty much match the Razr HD minus screen size & res. The M is a fantastic looking device and the size is pretty much that of the iPhone 5. I came from a 4S before the Galaxy S3 so the S3 was a nice change, reading webpages, RSS feeds etc but yes, it was too big for me. It wasn't overly huge, but I miss having one-handed texting and operation. The M is such a clean, beautiful device and I definitely like it much more than my S3 - especially since Jelly Bean has leaked for it and it is rooted. Internal storage is not a big deal thanks to MicroSD. My apps won't take up more than 4.5GB of storage.