They're really two completely different coats. As PhilB says, the issue raingear doesn't breathe quite as well. It is definitely bulkier, even more-so then its "Air Force" raingear counterpart. That being said, it is warmer then the stealth suit. (It has a thin liner). It is definitely not as tactical as the stealth suit because of its crinkle/noise factor.
Although the issue raincoat is an outer garment, whereas the stealth suit is "generally" used as an inner layer under the combat shirt, I find the "issue" raingear to be a much sturdier fabric, more resilient to random snags. (My stealth suit has some small snags even from wearing it under my combat shirt). The issue raingear also has reinforced elbows and knees (reinforced with what looks like Cordura).
I have both, and I believe, based on the weather, how long you're going to be outside, and what you'll actually be doing outside, both garments satisfy different requirements.
IMO, the new issued raingear is a good intermediary between "no coat" and the ICE/IECS coat. It is also quicker to put on and take off then the stealth suit (being that it is an outer layer). I would also prefer to wear the issue raingear during a downpour.
I also found, that by layering the Fleece with the Issued Raincoat, that I could keep warmer then if I was wearing just the ICE coat.
Eric
edit for grammar