What bykfixer said... under flashlight-type loads an NiMH cell is going to put out the same or higher voltage than an alkaline would.
Even if that were not the case, the flashlights are regulated based on LED current and temperature.
We're not saying that you absolutely have to keep your Maglite, just trying to make sure it's clear how well the rechargeable options for it work these days. At 1/2 amp draw an alkaline D has quite a bit less capacity than an NiMH D, and at a 1 amp draw I believe it goes below even an NiMH C cell.
In terms of newer flashlights there are a huge range of options, and AFAICS your choice will largely depend on what form factor you would most like to have. In general newer flashlights are smaller than they used to be, but "smaller" can go in a few different directions.
The smallest are based on 18xxx cells, with a single 18650 being the sweet spot IMO. Something like a Convoy S2+ would be a great entry point:
Smarter Shopping, Better Living! Aliexpress.com
www.aliexpress.com
Going up a bit in size there is a relatively stubby form factor option, typically with 2 18650 or 21700 cells. I don't like that form factor much but after playing with a new Mag ML25 2C I might reconsider that. The stubby lights are all over the map in terms of price and power/features so I'm kinda picking one at random but this gives you a good idea:
5000 lumens maximum output and 400 meters maximum beam distance. Three Luminus SST40 LED with a lifespan of 50,000 hours. Powered by two 18650 rechargeable Li-ion power batter...
www.fenixlight.com
I have had good luck with more traditional styles, eg 2AA format, although they do tend to "walk off" more frequently. I believe my last light in this format was an earlier version of the LD22 running on NiMH AA cells. Fenix now sells it with a single rechargeable lithium cell, but you can use 2 NiMH or alkaline cells instead if you want. Performance is limited with alkalines but IIRC not with NiMH cells:
800 lumens maximum output and 214 meters maximum beam distance. Instant activation with the tactical tail switch; output selection with the functional side switch. Detachable two-posit...
www.fenixlight.com
I talked about 2AA flashlights above but the same applies for 2 x 18650 "in line" - they're just longer, more like a 2D flashlight but much narrower.
There are larger flashlights (like your 2D Mag) but they tend to only be designed for higher power output (thousands of lumens) and so tend to be fairly expensive. Most of the flashlights you'll find these days are fairly compact but can still out-shine your Maglite... but I find that I really don't like using tiny flashlights because (a) they're too easy to lose and (b) they are too skinny to stand up safely.