A few things of note:
1) Relatively few monsters get any extra damage on a crit - most just maximize it, and minions don't even do that. Thus, it is less swingy in that you rarely have an enemy make an attack that, on a normal hit, would drop a PC unconscious - but on a crit, just kills them outright. You do have some PCs do this with monsters - but since they 'die' at 0 anyway (for all intents and purposes), it isn't as big a deal.
2) Crits giving flat amounts of damage bonuses (+1d6, 2d6, 6d6, etc) doesn't have the explosive potential that multiplying damage does. It also means that critical hits are important for everyone- whereas I've seen times when a rogue crits with a dagger is meaningless, but the full power-attacking fighter's crit will blow any enemy out of their shoes.
3) You can still design for some high damage crits, but the total limit is still reasonable. A level 15 character with a +4 Vicious Greataxe will crit for maybe 75 damage, as opposed to the 30 or so he might do on a normal swing. That's double damage from something tricked out to be good on a crit - whereas, previously, double damage on a crit was the norm. Someone tricked out to crit with a scythe would suddenly going from a 50 damage swing to a 200 damage swing. The only attack in 4E that really gets up there is Assassin's Point - a level 29 rogue daily power designed to be absurd on a crit. And even that at its worst isn't one-shotting elites or solos. It will only one-shot a regular guy, and only then if the character is really designed to take advantage for crits.
4) The frequency of crits is pretty strict. You crit on 20s. At epic levels, and rarely at the paragon tier, you crit on 19s. And in a few specific cases, characters can crit on 18s. In 3.0, you could be critting on 2+. And even in 3.5, which mostly fixed that, you could easily have falchion wieldings critting 1/4 of the time, starting at relatively low levels.
Crits are certainly still significant. They are still great to see happen. But I definitely think they have much less potential for abuse (from the player's side of things), and they are much less likely to spontaneously explode a healthy PC randomly (from the monster side of things.)