In my (entirely chairborne) opinion, the AN-94 was an ingenious solution to the effectiveness-at-range problem, but has been overtaken by other developments in small arms optics and ammunition.
The whole point of the AN-94 was to be able to put two rounds very close to the same spot in order to increase effectiveness, primarily at longer range (higher hit probability and better terminal effects), at the cost of increased weight, greatly increased complexity, and somewhat poor ergonomics. It did so successfully, and it is an ingenious mechanism.
However, after it was developed, small arms development went down a different path, solving the long-range problem with general-issue optics and improved bullet designs like Mk 262 5.56mm, both of which also improve close-range performance. A modern M4 with Aimpoint/Eotech and Mk 262 arguably gives better hit probability at long range than an AN-94 with iron sights, and it does so in all lighting conditions, without making compromises in the shorter range fight.
I've never handled an AN-94, but from the looks of it, it isn't very modular, it isn't much better as an optics platform than the AK-74, it doesn't look particularly light- or NVG- or magnifier-friendly, etc. The AN-94's weight (especially up front), length, bulk, and seemingly awkward placement of optics/lights would seem to make it *less* effective than the M4 in the 0-200 yard engagements that make up the majority of infantry combat. So while it might would have been just the thing in hypothetical 1980s engagements in Europe against 1980s NATO rifles and sights, it is IMO now outclassed by modern rifles that solve the same problems more elegantly and with fewer compromises.
