Pros
Some teams are independent, flexible, not micromanaged, but that seems to be changing. Expense policies are very generous and conferences, events, etc can be very nice. Benefits were pretty good, the HQ is very nice, and most people working there are helpful. I enjoyed working there and would only discourage developers and professional services people from avoiding Appian because you will have to make a lateral move if you leave. In sales, it is worth a shot since the potential market share is high.
Cons
They verticalized territories way too early. Their core industries carry them, so if you aren't in financial services or federal then you will struggle. Only AE's with happy, cash flow rich Customer Accounts will hit their number regardless of industry. Only 10-20 AEs are hitting plan across the company, and they've almost all been with the company for years. One of the "rainmakers" was on a performance plan after ~2 years, and happened to close a deal with a huge FS firm and now he's always at the top of the leaderboard. The product is not as good as management makes it seem. The competitive intelligence is extremely biased. I heard from a customer who I had a personal relationship with that one of the competitive intel items was simply not true. The CEO sent an all caps email out after a negative Gartner report which took them out of a key quadrant, saying that "this is actually a good thing". They are very arrogant, and totally unwilling to swallow their pride and start winning market share. They will remain a niche player unless they change that. They say they're the only platform that has their key components, yet somehow it is a very cluttered space they sell into. Some AEs stay there 3+ years without closing a deal. Legal and pricing torpedo deals all the time.