Glass essentially turns everything into a 1 Hit kill instead of just Melee.
The maps are not designed for good cover so there is always flanking fire.
If you have a Fireteam without a Titan (or 2) it gets really nuts.
Most strikes you can't get a good strat going until the 3rd or 4th wipe. Never mind when the enemy fire matched the Singe burn type.
Blackout modifier is a piece of cake next to Glass IMHO.
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I think it depends on the strike. The thrall running around on savathuns song during the boss fight make blackout hugely difficult to deal with. The only other thing I'd add, is glass will get easier as you level up, blackout won't.