As a DM (and not a player) I like those early levels (maybe 1-4), and as a stat freak (see sig) I keep all manner of odd notes- my present gaggle of players have accompanied me through (I think) 16 scenarios since the start of the year (with them playing out a number of campaign arcs)- so the same players are running agroup through Wizards Core adventures (approx. 60% through P1 atm) with a different set of PCs through the Scales of War AP (just finished the 4th scenario) and through some other pathways cobbled together using Goodman Games scenarios and the like.
I've found it slightly harder to judge how encounters are going to play out as the PCs level- obviously using bought material that's not a big problem however it troubles me when what I thought would be an easy fight turns into a tangle, while the climax (my PCs just killed Skalmad, King of the Trolls and a couple of Warren Trolls and Nothics- their first encounter with Skalmad, in two rounds). Most often it's the case that the dice go against me (at least that's the story I'm sticking too). I've had encounters where a player has made three Crit rolls with an area Burst Spell and basically decimated the bad guys in the first round.
I spent a session the other day rolling nothing above a five- honestly, it was riduculous.
At the lower levels I feel I'm always in with a chance (of killing a few of them- that's not my intention overall but those tense moments- particularly at the climax of the adventures are very memorable).
Maybe my players are much brighter than me, don't get me wrong there's not a bad level of play in 4e (not that I've found- good friends and a great game always make for an entertaining evening) but the lower levels are often more dangerous for my players.
Higher levels brings drama and intrigue, with the twisted campaign arc playing out.
Lower levels mayhem, limited choices, and carnage, significantly I've killed maybe ten PCs playing through the 16 scenarios-
Lvl 10 x1
Lvl 4 x1
Lvl 1 x8
Lower levels are in comparison imho blood-soaked, and oft times thrilling.
The OP stated that they couldn't find any low level monsters, I keep a table of every creature the PCs have killed (in all adventures) to date, hang on... just go and find it.
Not including Minions there are-
21 x different Level 1 Monsters,
26 x different Level 2 Monsters,
36 x different Level 3 Monsters &
28 x different Level 4 Monsters.
More than enough, and at Lower Levels I find the Elites and Solos are worth their weight in gold (for me- my players may think differently, ask them about their first Gelatinous Cube, or their first Insubstantial enemy, or Irontooth)- at lower levels monsters can really stick around and prove troublesome.
That said the highest Level I've DM'ed is 12th so maybe I'm in for a surprise down the line- nothing bad to report so far though.