If you're a fan of the JA series, BiA is definitely worth your time and money.
But for old-school gamers and fans of JA2 (of which I am both), JA:BiA is a very good remake of JA2 and easily worth the 40 buck asking price. While it's not a 9, it's certainly better than Gamespot's score of 5.5 indicates.
Reasons why it's better than JA2:
Better graphics and weapon effects (shotguns kick up clouds of dust, grenades leave smouldering shrapnel spots that fade after a few seconds, bullet holes appear on objects)
Requires LESS patience (believe it or not)
Quasi real-time control scheme works well once you've gotten used to it and is a much better option than a strict turn-based solution. Plus, no waiting for enemies to take their turn.
Health cap drops sharply when mercs are injured a lot in a short period. While this does seem annoying (and it really hampers strategy if you use a small squad for everything, like I am doing), it's a fairly reasonable limitation to impose. Mercs only heal "properly" if enough time passes. It also forces you to consider getting more mercs as a backup squad, or decide to soldier on with what you have. As low-health squaddies are even more fragile, more skill and strategy is required to win battles.
Character development is tangible. It's possible to take an average merc and turn them into a sniper over time, like I've done with MD – he's now the best sharpshooter in my squad after a bit of levelling. Ira is coming along nicely, too, and she was very poorly-specced when she joined.
Merc actions can be synchronised, making it possible for 2 or more mercs to attack the same enemy, at the exact same time, or for them to fire only once both are in position.
Reasons it's the same as JA2
Big list of mercs to choose from, each with their own personality and equipment
Tons of weapons
Same "free Arulco" over-arching mission
Lots of side-quests
Micro-management of a merc's inventory (yes there's a lot to do but I enjoy it)
Armour deteriorates quite rapidly and requires you to always order in more or scout around for better stuff than you have.
Laptop-based merc recruitment, supply purchasing, e-mail conversations between yourself and your employer.
Success will require you to save and load a lot. I considered not doing this but honestly, I could not afford to replace mercs as often as they died. Load times are about as long as I remember them being in JA2 even on a Core i7 system w/lots of RAM.
Very similar (cheesy and often funny) voice acting and dialogue. It effectively conveys the same B-movie feel of the other JA games.
Mercs don't all get along, which plays out in the dialogue.
Reasons why it is worse than JA2:
Can't train militias in a captured town/area by leaving a merc there and setting them to the task
Each new militia needs to be given a weapon in order to join your cause (I suppose that's also "realistic", just wish I could also train them afterwards).
No fog of war – you know where all enemies are, all the time. While a significant departure from JA2, this in no way makes the game easy – it's still quite a challenge.
No way to add more militia to an area. If there are only 3 that can be recruited, that's it.
One issue that I can't address in the better/same/worse manner is the camera – it's not broken because it works fairly well, it just doesn't give you total freedom of movement to check everything out from any angle. I would like to see a better viewing distance and a better overall frame-rate when angling the camera such that I can see off into the distance, but apart from those gripes the camera does what it's meant to and I don't believe the game score should be penalised for it.
These are my impressions so far, and I'm about 30 hours into the campaign and have only just taken Grumm. As such I can't comment on the end-game, but so far I am really, really enjoying my time in 3D Arulco. It's got the same JA feel, and the new touches don't detract from my enjoyment or have me sighing nostalgically at how much better JA2 was.
My final word is that if you're a fan of the series do yourself a favour and pick this game up – its new 3D presentation, manifold charms and somewhat old-school feel are well worth your money, even if it's not the polished, AAA gem our dreams would have liked it to be.