Unfortunately I cannot compare well to Harpoon as at that time I was not a big fan of similar games. The review says it's a sort of better Harpoon 3 but it's difficult for me to say for sure, I did not play Harpoon 3
I think this is the first one from Naval/Air genre that sparked my interest.
So far I can only say that spotting/radar/sonar contacts seems to be done well basing on speed, if something is blocking the view or not (mountains, horizon), radar/sound signatures, thermal layers for subs etc. There's a lot of factors. The AI is not bad at performng tasks you assign it (partrolling, employing weapons on targets you specify - though you can go manual on it - or at defensive tasks). You can also do a lot of things by yourself planning missions for units, plotting courses, speeds, altitudes, using weapons you want exactly etc. Missiles and other weapon and defence systems behave is a believable manner (guidance systems, missile paths, fuel, energy etc.). Land combat is lacking but it's not the main focus of the game so that's understandable.
The database is huge indeed, you can have scenarios starting from the 50s up to nearest future (2017 for example), all with proper ships/aircraft/weapon systems. It has several thousand real world ships, aircraft and weapons in it. There is also loads of preprogrammed airbases for example, all with the same building layout as in reality, pretty neat.
The game seems to fairly well represent these kinds of things I think. I'd say the game is pretty realistic as a simulation of these ops, very complex under the hood and yet not a nightmare to play UI wise for example. So it can be very fun and I'm thinking it might be even more interesting in multiplayer when you play against a cunning human being
But I guess it's best if you read some reviews, watch some movies on youtube as the game is quite expensive and it's better not to make a mistake and buy something you would not like
You need to like this type of wargames.