Fallout 3 is easy. Especially after playing New Vegas with hardcoe mode, perk every two levels, traits, and other features. Operation Anchorage is to blame
I love that DLC but I never do it on low level characters due to the overpowered stuff the armory holds, such as "unbreakable" T51-B PA and the Guass Rifle. Plus the story line is linear and options are not seen as much or intended when looking back and when compared to NV's superior storywriting, it can/will make Fallout 3 look easy only by making it look dumbed down.
Broken Steel, though my least favorite DLC, does add the up'd feral ghouls, overlords, and rad scorpions which are okay but not a great challenge as they may have been designed to be, except the ghoul he is a bullet sponge and not a "fun" enemy to encounter.
I found that after the main Broken Steel quest are completed, all side quests completed, all unmarked quests completed, every unique item gathered and all achievements received, there was really nothing left to do in Fallout 3 other than wander around and collect randoms items. Maybe it's just me, but I found the lack of minigames in Fallout 3 to be a turn off (the text adventure game in Hubris Comics is fun, however, it only lasts for a little while.). In NV there was minigames such as Blackjack, Roulette, Slots, and Caravan to play which definitely enriched the experience.
One other thing about Fallout 3 is that once you have a lot of caps, there is barely anything to spend them on. It's rare when you see something that costs more than 2000 caps, while in NV some items can cost a minimum of 6000 caps. Definitely makes you want to make more money.
Edit: It's also pointless how some fully repaired items are worth much more than the amount of caps a vendor will ever have. For example, a fully repaired Plasma rifle is worth 1799 caps but yet almost no merchant has more than 500 caps in their vanilla inventory.