It works really well in Hell's Horses units.
What you've got to realize about the original Athena is that its the typical glass cannon that most Clan vehicles are. Fortunately, when you use it with the Hell's Horses combined arms units, your opponent usually has something that's more important for him to shoot at than the Athena (like a Hellstar in his face).
With that in mind, the original's strengths are obvious. Twin Gauss rifles with a targeting computer, with twin ERMLs and MGs, and a LRM10. The Gauss rifles and LRM10 can fire forward, while the ERMLs and MGs are turreted so you can keep track of units trying to flank you. The MGs give you the ability to keep infantry off of you (and in eras when not all designs were made with TW rules in mind). Even the ammo count for the GR is pretty good.
The downsides are equally obvious. The Gauss Rifles ONLY fire forward, so you need to hang back, and of the design has Clan vehicle levels of armor. The BV is hefty as well.
Keep the Athena in the background, lobbing in GR and LRM shots, and you should be fine. With `Mechs up front pushing in, your opponent is going to have a hard time dealing with the Athena.
The HAG variant is...well, pretty much just more of what the original is. The GR's have been upgraded to HAG30s, doubling the potential damage (You lose the solid hits, but the amount of hits makes up for it IMO). You can also use the HAGs to deal with aerospace or VTOLs. The ERMLs remain the same, while the MGs have been replaced by APGRs, letting you hit at 3 times the range. The targeting computer remains, and you've got an ECM suite to hamper your enemies, either through cutting off their advanced electronics, or by making it harder for them to hit via ghost targets.
The downsides are somewhat similar. The BV of the HAG variant is well into the Clan Assault `Mech range. The HAGs have smaller ammo endurance than the original GRs (12 compared to 16). The HAG's are fixed forward.
Like the original, its a good, hard hitting design. If its worth 2400 BV is something that's up to you. Just realize the main limitations is that its guns are fixed forward, and keep in back where it won't get swarmed, and it will send in shots all day long.
For what its worth, most of the Hell's Horses designs are solid. I think the only ones that people question are the the odd XTRO designs and the "upgraded" Enyo from TRO:Prototypes. :)