And here comes my humble opinion (probably slightly biased since I'm sitting in Irving, Texas attending school at the NEC HQ... hehe)
The 2400 is a truly remarkable system. Yes, programming it is a pain, and requires a number of things, including being able to convert from binary to hex when programming. However, in my first week of class, I built, cabled, and programmed a 2400; not bad considering I had never seen one.
Meanwhile, it's phenomenal... the VLSI integration assures that you will NEVER get a ROT from lack of paths; the NEC has, for years, used packet switching, so everything has always been digital.
The system is nothing short of mind-boggling. Let me give you a taste;
Each PIM can support 384 lines (288 physical lines come out in 12 25-pair connectors; the rest are internal for T1 cards, etc.). You can have 4 pims in a stack (1536 lines), 4 stacks in a "wall" (6144 lines) and 4 walls joined together (24576 lines).
It has full redundancy capability; dual processors, dual power supplies, dual MUX cards, etc. It can be clocked internally, externally, and will fall back if clocking goes down (say your T1 takes a crap).
I am, personally, quite impressed with the system. It's INCREDIBLY versitile (which I've seen just from going through the job spec manual, where you turn on and off all the features), and integrates smoothly with VOIP and networking.
Just my $0.02
"In order to start solving a problem, one must first identify its owner." --Me
--Greg