I worked 5 years for AxxonSoft, now I'm designing systems, mainly with AxxonSoft and aimetis.
AxxonNext, already tested here, works fine in smaller projects, but is also already used in projects with a higher amount of cameras (400, but no special features).
Axxon Intellect is in use in project sizes from two to a couple of thousand cameras. Me personally worked on projects in the UK, Sweden and Germany with couple of hundred cameras. One project in the UK contains 350 5MP cameras (not my decision!), main challenge here was HW ;)
No SW will be just run out of the box. Intellect needs a deep training and understanding, but this is the same for Milestone or Genetec. Beside of the already mentioned advantage, I see the advantages mainly on flexibility. GUI is something you (client) decides. Basically, Intellect could look like always different, depending on who is logging in, where are you logged in, when you logged in. Yes, it is complex to configure, but Flexibility means most of the time you need to tweak things - and you should now what you are doing.
Intellect works (especially) fine on Distributed Systems, like for Companies with different locations but mainly monitored from one location. You also have the chance to add other subsystems (like we did with Access Control or Intrusion Detections systems (e.g Paxton, Salto, Optex...), you can add LPR or Face Recognition (me personally did both) as well as several POS-systems.
Any special questions, feel free to ask.