While I can't buy loot boxes in World of Tanks on account of them being considered "gambling" in Belgium, I am able to receive them as gift. So I got 25 loot boxes from the current holiday event of World of Tanks, which enables me to better judge them.

Wikipedia defines loot boxes as "a consumable virtual item which can be redeemed to receive a randomized selection of further virtual items". If you apply that definition strictly, every booster packs in every collectible card game is a loot box. However those card booster packs are a lot less controversial than loot boxes in other games. Why is that so? The answer lies in what happens if you have bad luck. What do you get if you don't get the "randomized further virtual item" that you were hoping to get? In many games with loot boxes, you might well get only stuff that is absolutely useless to you, e.g. a skin that you don't want to wear and that you can't trade away. The loot boxes in gacha games can contain low rarity items that don't help you at all in the game. The booster packs in collectible card games usually have guaranteed rarity distributions, so you don't need luck to draw a rare card (you still need luck to draw the rare card you wanted).

The World of Tanks loot boxes work a lot like booster packs in that they have a guaranteed content, which is 250 gold and a tier V holiday decoration. Which means that if you buy 25 boosters for 40 Euros, you at the very least get 6,250 gold, which would already cost you over 20 Euros to buy directly. And the holiday decorations also have value, because they raise your "festive atmosphere" level, which in turn gives you a bunch of other rewards. In my case, in spite of having come to World of Tanks after Christmas and thus missing much of the event, the 25 loot boxes were just enough to max my festive atmosphere level to 10 and get all 4 female crew members, tons of consumables, and several million silver worth of discounts on tank purchases.

And then of course if you open 25 loot boxes, chances are that many of them contain more than the minimum content and a few contain high value content. In my case, I got 9,000 gold, 17 premium account days, 2 garage slots, 2 unique styles (skins), 1.9 M silver, and two premium tanks: A tier V medium, and a tier VIII heavy. Now except for the unique styles, you can buy all of this stuff also for money (to be precise, you can't buy the exact premium tanks I got, but you can buy other tanks of the same type and tier). So you can calculate back the "virtual value" of the content of my 25 loot boxes, which in my case was about 100 Euro (not counting the holiday decoration). And I think the tier VIII heavy was my only really lucky draw. So 100 Euro is virtual value for 40 Euro in loot boxes is not a bad deal, in my opinion.

The obvious caveat in that calculation is that one probably wouldn't have bought that particular collection of virtual items for 100 Euros. I wasn't likely to spend 12,000 gold on a tier VIII heavy IS-3A, as I already got a tier VIII heavy Löwe. However the majority of the stuff I got, gold, silver, premium account days, and garage slots are universally useful, and already worth more than the cost of the 25 loot boxes. Which makes me think that if bought in moderation, World of Tanks loot boxes are close to a guaranteed good deal rather than gambling.