My 2 cents on Presonus's position in the market is this. From January of 2009 until what, maybe middle of 2012, they had no real competition. The only other mainstream product at near the same price point was the latest iteration of the Yamaha O1V. I was surprised that for over 3 years virtually nothing came along to compete. It allowed a company, one with no experience with live mixers, to come in dominate the small format mixer segment. My guess is part of this was perfect timing. They'd done all their R&D and tooling just before the recession. By the time the mixer hit the streets companies were strapping in and not really innovating much beyond adding powered speakers to their fleets.
Fast forward 5 years since release and there is fierce competition from the likes of A&H, Soundcraft, Behringer, Line 6, and Mackie with offerings $1000 - $3500. Most of this has really popped up within the last year. Presonus has chosen the Yamaha 01V route and kept the format of the mixer basically unchanged, but added additional bells and whistles. This is pretty much what they've done from the start. When I first bought my SL 16.4.2 in Jan of 09 there was no ipad mixing, no smaart, etc. I still think the format of the SL is very good as far as providing the benefits of digital features with most of the tactile comfort of analog. It's learnable in just a few minutes and a wise choice as a bridge to digital, particularly for install situations where multiple users have to master the board. It was extremely innovative when it came to market and that sizzle lasted for a lot longer than I thought it would. It's simply not the sexiest thing anymore and, in its current form, they can't get that edge back as the features are capped by the physical controls of the mixer itself. Many of the new players can pile on functionality via built in touch screens and tablets.
In March of this year I bought an SL1608, originally as a backup, but haven't used my SL since. The only thing I truly miss from the Presonus is the multi-tracking, which I absolutely loved. It basically paid for the mixer in that the demos were cut from live shows saving time and money versus going to a studio or buying stuff you'd not need otherwise to record a demo. It also really taught me how to mix as I could sit down in my own home and relive the show as the tech instead of the lead singer. I could experiment with compression and especially EQ and really came to understand what I'm doing when crafting a mix.