Has anyone else noticed that if you start exploring the wasteland at an early level (I did this after leaving Vault 101) that the game spawns the weak enemies (Mole Rats, Bloatfly, Mirelurk and radroaches) nearly everywhere? (Apart from set locations like the D.C. Ruins, Old Onley, Raider bases and robot areas, even though you'll still get the weakest variant of these).

It was weird making my way to Fort Constantine and just see Prototrons wandering about the place, with Mole Rats and small Radscorpions spawning in the areas around it....

Makes me wonder whether exploring everything at LVL 30 is actually harder than say, LVL 5 because you have Overlords, Reavers, Mirelurk Hunters and Sentry Bots.

As you go through the game, the enemys will level up with you. After a certain point, they will spawn mutiples. There's nothing like fast traveling to somewere and arriving with 4 albino rad scorpions attacking.
Or going into a drainage pipe and encountering 5 ghoul reavers.

First time I ever played Fallout 3 I was just about to walk into the parking lot of the Super Duper Mart when I saw a Deathclaw in the middle of it. It was my first Fallout so I had no idea what it was and here I was at about level 3-5 with a 10mm Pistol. I killed it, but needless to say i [censored] my pants.

....

Yeah, I noticed this on my sort of 2nd playthrough and wondered whether I could go to the North part of the map from the start, worst thing I ran into were normal Mirelurks

On my 1st though, the enemies get real annoying and I also did most of the DLC's at 30....bad idea when it comes to MZ and PL, I'm sure those Tribals and Swampfolk level up with you

I did the same thing with MZ, PL and the Pitt. I got my behind handed to me a few times by the swampfolk and the reavers in PL. I had to reload Plik's Safari a few of times also.

I used to run hellbent from the 101 exit to Fort Constantine to kill that lone Enclave trooper and grab his armor really early. God that was fun.