Pros: Build quality, responds well to mods, good bass response, price, detachable cable, easy to drive
Cons: Extremely uncomfortable stock, can be muddy, mids recessed, small soungstage, crap cables
So I am fairly new to the audio world. The Monoprice 8323 was my second purchase on starting to get into headphones (after Superlux HD681 EVOs). I have had these headphones for about 6 months now.
First the bad things about them. The cables and pads are the let downs in terms of build quality. There are two cables. The first is really long and cheap feeling. It also has pretty bad microphonics. The second is a mobile cable but it is literally the thinnest cable I have seen and feels even cheaper. Fortunately since they are just standard 3.5mm stereo to 3.5mm stereo cables they are very easy to replace. Monoprice has mobile cable on their website for $3-$4 (depending on length) which is a big upgrade on the stock ones both in terms of feel and microphonics. The pads are very uncomfortable and cheap feeling. The soundstage also isn't great. Due to the pad and tight clamping force, I could not wear these for more then 30 minutes at a time when I first got them. In terms of sound quality, the two let downs for me are the bass can be too much and make some songs muddy. The mids can also be recessed.
Now the great things about them. They are sixteen freaking dollars and for that price you'd expect completely crap sound quality and build quality but you don't get it. They feel well put together (better then the Superlux HD681 EVOs) for the most part (minus pads and cables). There is plenty of bass and the response is good. The highs are fairly crisp. They are easier to drive then the Superlux and offer fairly good isolation. The other great thing about these headphones are that they are easy to modify and respond well to the modifications. See this thread. http://www.head-fi.org/t/610542/mod-monoporice-8323. Brainwavz HM5 pads fit and do wonders for comfort and the sound (reduces bass fixing the muddiness, brings out midrange). The angled HM5 pads I found improved the soundstage as well.
So if you buy these, I'd suggest the following mods for sure; the Monoprice mobile cable ($3), Brainwavz pads ($22) and leaving them stretched over something over night to fix the clamping force. The problem with this is then the total cost is $42 which is more then the Superlux HD681 EVOs which I think sound better or the Superlux HD668b which I like way better. That is ultimately why I gave them 3.5 stars.
I'd suggest the Monoprices for two groups of people. Someone who wants something inexpensive that is more portable and offers better isolation then the two Superlux I own or someone who wants a pair of headphones to play with and modify.