General Comments:
The best 4x4 on the market with great off road capabilities.
Very comfortable to drive for long distances with a good high driving position.
200 TDI engines are by far the better although a little bit loud!
If buying look out for one with a service history as these vehicles really need there servicing to be kept up to date. Regular oil changes on all those parts that need oil (an there are many of them on a Discovery) is the key to reliability.
Look out for worn gearboxes as these are expensive to replace.
If buying make sure the cam belt has been changed and if not change it yourself quickly for peace of mind.
All running gear (steering, suspension, axles) should be checked if buying secondhand as problems will start to arise in a vehicle of this age.
I love Discoveries as they are by far the best 4x4 on the market today.