Vantaggi
Appian takes skill and talent very seriously -- promotions are given based on ability, not on politics. Even if you're young, if you work hard, it will be rewarded. The CEO still interviews every hire personally to make sure they'll be a good fit with the company culture. The overall culture is fairly young and vibrant with happy hours, etc. While smaller than competitors such as IBM and Pegasystems, the company is rapidly accruing new customers and revenue, and seems to be on an upward trajectory. The technology is very cutting-edge; things are never stale around Appian.
Svantaggi
BPM is still fairly obscure in the software/services industry -- you'll get a lot of blank looks when telling people what you do. While the company has improved internal recognition (intra- and inter-departmental awards are given out every quarter), it tends to be the same small group of people who get recognized the most often. Departments like marketing and corporate do not get the same respect and perks as the technology and professional services depts do.