Was the tombstone banishment a recent change? I thought that'd been around for a while...
Was in a co-op game recently with a guy trying BM for the first time. After a few deaths he said "I'm just going to AFK from now on... Not long I can do much else with this piece of shit hero".
Now, I'm certainly not a good Beastmaster; my micro skills are just about put to the test on Skeleton King. But even I can realize that Beast has some very nice gifts to grant upon his team, not the least of which is his amazing superward/'Naix on a Plane' delivery system. That ult is just fabulous, and his axes are a basically powershot that doesn't require channeling and doesn't decrease in power just because it annihilated the creep wave before lopping the head off a fleeing enemy. I managed to convince him to push on and to give BM a few second chances before putting him to rest for good... Hell, I once managed a co-op as Visage and maintaned a positive KDA, and I've already mentioned my micromanagement skillz (or lack thereof... Touchpad doesn't help).
Personally, I think Necro is actually a really good item... Or at least it would be if it cost a fraction of its price. But it doesn't. Necro 3 is 5200 gold total. That's 100 gold less than a Refresher, and all the annihilation that can provide. 150 less than Assault Cuirass. It's more than Vladmir's Offering and Mekansm COMBINED.
You're talking nukes (by the way, max burn on Archer is 225, not 300. Anybody know if that does pure or just magical?), Dagon 2 is less expensive by over 1000 gold, does over twice the damage and has a shorter cooldown.
Invis detection? Yeh, because 200gp Sentries or 180gp Dust is for people who don't know any better (I will admit though, it is nice to have as kind of a sideline thing, when you aren't expecting an invisible dude to show up but want the creep anyways).
DPS? Sure, they can deal some damage if you let them... But thing is, people aren't going to let them. They're pathetically squishy for when you get them on the field, they're not your main hero and as such will probably not be managed as well, and they have a bizarre tendency to get stuck on things as a result.
The aura is only nice because it stacks, just about every aura it does stack with is superior in some way. However, those other auras are passive auras that are constantly active (except for Drums, the passive for which is actually inferior to upgraded Necro aura. The active by itself is superior to all levels), whereas Necro aura is only available for a maximum of 45 seconds on an 80 second cooldown. Pick your battles, apparently...
Plus, these dudes have a 100 gold bounty... That's the same as Warlock's supertank golem. Just on 400/600/800 health and 6/8/10 armor. Now, those values would actually be pretty impressive early game... But you can't get the impressive values early enough because of how prohibitively expensive it is.
I'd probably build Necro more if I thought I could handle another activatable item and could micro the minions... But just as it is, I think it's a perfectly decent, reasonable item that's ridiculously overpriced for its effect. A bit like Radiance, in that sense.
Interesting point of note: Minions have the same vision at night as during the day, being 1300/1400/1500.
EDIT: Completely unrelated note, but as of this edit there is one hour left of the amazing Humble Bundle 8. Hop to it.