A lot will depend on the vehicle you plan to swap the engine into. I have a 4BD2 in a 60 Series LandCruiser and it is outstanding. But, there are many issues to contemplate.
The 4HE1 has the starter facing to the rear on the North American passenger side foot well, they are electronic control engines, have a different bolt pattern on the sub bell housing than the 4BD1/2.
The 4BD1/2 are mechanical diesels that only need the starter and alternator connected to run. Starter faces forward and adapters are available to make the rear of the engine into a Chevy V8 bell housing bolt pattern.
Common issues - These are tall engines, and heavy engines compared to a many gas 4 and 8 cylinder engines.
Good things - I have averaged a little over 20 mpg during about 35k miles of all types of driving. Parts are available at any GM or Isuzu dealer in North America. These engines were designed to push around box trucks that have a GVW of 17,000 pounds, so most things we swap them into weigh considerably less, so last a long time.
Read my build on the link below. Check IH8MUD and 4BTSwaps.com in the Isuzu section for great info on these engines and how they are maintained and swapped.