I fly NWA almost exclusively out of MSP. Aside from a few Airtran, USAir and Midwest flights to the east coast. NWA has NEVER changed a flight on me by more than 15 minutes. And, when the flights were changed I was notified by e-mail. I always trust that the flights will be exactly as stated. In terms of reliability, they rank at the top of my list.
I wish they had the price credits that SW has, but unfortunately, the price you pay is the price you pay-period. For that reason, I always keep an eye on farecast because they seem to have a good handle on when NWA is going to drop or raise their prices.
I will be using them again in May and most recently used them in October. The flights certainly were no louder than any other flight I've been on and I don't anticipate them being any worse in May.
Additionally, one thing I do like about NWA that some people may disagree with is that you can pay a small fee to reserve an exit row seat. Now, you also have to pay a small fee to reserve an aisle seat in some cases, but in reality most people never do that. I like the freedom of being able to get the exact seat I want without having to worry about getting to the boarding gate area before any other passengers just to reserve said seat, this way I can do it in advance and just pay for the convenience. To each their own.