Lucky you!
Initially, the TDCi engines got quite a bad reputation for reliability, and there were some problems with the gearbox not being man enough for the job - but these issues have supposedly been fixed now.
The interior is a big step forward from the TD5 - except for one thing, they have decided to remove the front flappy vents in order to accomodate the new dashboard. That would be the only thing I'd really miss about the earlier models if I were lucky enough to be in the position to buy a new one. But, comfort and ergonomics wise it is miles ahead of previous Defenders.
Bear in mind that an all new replacement for the Defender is due in 2012, so I'm not sure if you can wait that long but it might affect your decision.