What IXes is it at? Its IX presence and where the core of its network originated will tell you a lot about where its network is strongest. What kind of services does it focus on? Residential? Commercial? Carrier?
Does it have other ASes that are owned by the same company and are downstream subsidiaries? How many other smaller ISPs look like they're buying transit from it, or is its AS a stub?
Have you met any of the ISP's people at a previous NANOG conference? Do they sound like they know what they're doing? Are they building something interesting and modern?