It renders Streaks impossible to fire, it turns LRMs into "TAG or NOTHING", and it utterly buffaloes targeting outside of nose-picking range. This is very effective in making the game into brawl and sneak mode. And the only effective solution is another ECM (or multiples, if they have more than one).
That's overdoing it. Let's look at the problems ECM is "fixing" and what went wrong here, and how to fix it.
Streaks: Streak Cat. 6x streams of can't miss missiles. Scout murderers. Endless barrages of gnawing damage no other 'Mech could manage accurately with ballistics or missiles until enemy fall down, go boom...
...until ECM came along and rendered them from magic missiles to inert weapon systems that can't fire. At all. Here's where ECM went too far- it doesn't allow Streak SRMs to fire as normal SRMs when jammed.
Streak fix: Streak racks with an ECM'd target or inside a hostile ECM fire their Streaks as normal SRMs instead. The superaccurate shot is gone, but the missiles remain able to fire. What, a Catapult armed with equivalent of two overweight SRM 6's is somehow broken when we have ones armed with SIX?

LRMs: LRMs being able to rocket in from immense distances beyond which most 'Mechs can't deliver accurate fire back, Artemis/NARC/TAG creating uber-deadly strikes.
...until ECM came along and the only way an LRM can be fired at ECM'd targets if you keep TAG on them, with even the slightest interruption breaking lock again- a bad deal vs. lights that can easily interrupt TAG repeatedly for brief periods of time. Say, going in circles around another 'Mech? Alternatively, dumb-fire the incredibly slow rockets and watch a result that makes an LB-X shot seem OP as your missiles scatter wildly.
LRM fix: Give ECM 'Mechs a no-info red bracket when R-locked from 201-400m away, up to 500 or 600m (leaning strongly towards 600m) away with BAP. Double lockon time and halve the amount of time a 'Mech can be off-crosshair before losing lock, based off standard LRM times. Give no bonuses for Artemis, NARC, OR TAG when firing at an ECM covered target or if inside a hostile ECM bubble, determined at time of firing and not changing if ECM is cut off mid-flight. Suddenly, LRMs are much like they were in earlier closed beta when they only had a 600ish range- unable to stand-off at long ranges and bombard the entire map at will, meaning non-LRM 'Mechs have much more opportunity. The fact that ECM lets them GET closer without even being spotted doesn't hurt, either, and many direct-fire weapons are quite effective retorts at 400-600m.
Targeting: ECM blinds even IFF, leaving PUGs often utterly confused as to what to shoot at- heck, even some premades as nobody's red OR blue. Meanwhile, the team with ECM on their side knows exactly who to shoot and where to shoot them.
Targeting fix: See "LRM fix" above. From 201-400m (500-600m with BAP), hitting R will result in an enemy having a red enemy bracket around them, but no data otherwise. No chassis ID, no weapons list, no damage paperdoll, not even an "A to H" letter designation. 'Mechs are still tough to spot without BAP, and still gain stealth bonuses from ECM - just not as incredibly difficult to actually figure out who's good and who's bad in the increasingly common furballs ECM has caused. Of course, at medium to long ranges people will STILL be confused and unable to lob LRMs in- but it's no longer insanely perfect.
Edited by wanderer, 06 December 2012 - 03:27 PM.