OldCom is nice simply due to the expendability of soldiers and the incredibly low requirements to get quite functional weapons going. This makes the battlescape part of the game much easier.
A new recruit with a laser/plasma pistol, a medikit, and some smoke grenades and flares is often your man of the match. You can complete the game reasonably easily with just laser rifles. Plasma weapons are incredibly easy to research and are very abundant (anyone, no matter their stats, with a plasma rifle or heavy plasma can take on anything). You start out with massively destructive rocket launchers (and heavy/auto-cannons). Stun rods are the only option for captures for ages, but again, are very early-on in the tech-tree. Your starting craft has a massive troop compliment too, although it's a horrible interceptor (it's ridiculously good without the 80 item limit in OpenXcom).
Basically, you get the tools to succeed very early on. Sure, you'll lose plenty of men. But as long as you can get the next rookie on board a skyranger, give him the biggest, deadliest or cheapest thing you have laying around, they're an instant super soldier, even if they are a glass cannon.
No leveling, no decision making, just give them what you want and run them through the grinder. OldCom recruits get a lot of flak for their stormtrooper-like accuracy, but they do come fully trained for any role, be it sniper/heavy/CQB/grenadier or medic. And they can do it all in one mission if required. If they survive, they'll get better. At everything! Strength and TU are your "better at everything" stats, and doing nearly anything raises them. Enemies might seem harder, but you can dish out the same amount of instant death as them, yet only take the same amount. Next super soldier, step right up! The world needs you...
Armour, craft and craft weapons all come in a bit later. But it's really simple to get profitable things to manufacture, the timers are pretty lax as soon as you do, and even with a total squad wipe where you lose all your goodies, you can just send in a new squad with rocket launchers and smash'n'grab for some new toys whenever you need to (assuming you left someone in the skyranger to bail out of a mission when needed).
Honestly, after playing X-piratez and realizing that some of the techniques you use in that are just as applicable to OldCom, it seems a lot easier. But there's no research malarkey or tech-gating, no "must-do" missions, no real timers, just tonnes of cheap recruits on a huge replaceable transport with super-weapons (and even superer weapons available at a moment's notice).
TftD is a bit harder, with underwater/above-water weapon differentiation, more tech-gating, and generally scarier stuff to fight/the AI they use, but it's not all that different once you work out the basics.
OldCom is really quite relaxing and enjoyable compared to NewCom or X-piratez. No stress, no hassle, just nuking entire maps from day 1, followed by accurate sniping/CQB and captures shortly afterwards, and maybe a bit of heavy armour or voodoo shenanigans after that. It's refreshing