An engineering game, as I'd define it, is a game where a primary gameplay element is designing machines for some purpose, weighing conflicting needs such as cost, versatility, and performance. I've only played a handful of these games, and I really wish I could find more. Here are some of the ones I've enjoyed:
Kerbal Space Program: I'd call this a definitive example of an engineering game, and one I have hundreds of hours in. I absolutely love designing rockets, figuring out what I'll need for each mission, experimenting with different staging mechanisms to maximize fuel efficiency, pushing my available tools to the absolute limit to land on far-off celestial bodies, etc.
Automation: The Car Company Tycoon Game: Yes, I know, fuck cars, but I'm having fun with this one. There are a lot of different niches you can cater to, and I enjoy specializing in affordable, reliable, fuel-efficient sedans and compact cars against the trend of turning everything into a gas-guzzling behemoth.
Master of Orion: Yes, a DOS game from 1994, and primarily a 4x, but its ship designer has some of the best balance between simplicity and depth I've ever seen. Ships have a limited hull capacity, but no fixed number of weapon hardpoints, and they can only fit a handful of special modules, but there are dozens to choose from, with widely varying capabilities. The number of actual choices to make is small, but they involve balancing so many things - durability, damage reduction, damage output, armor penetration, weapon range, maneuverability - and the turn-based combat gives enough control to let you really appreciate the impact your designs have.
Avorion: A space flight sim with highly customizable ships built out of blocks, with fine-grained control over things like engine power, maneuver thrusters, and armor thickness, and cargo bay sizes. I wanted to like this one, but it's way too grindy for me (building up your reputation with factions takes forever, and they won't let you buy better ship equipment until you do).
Robocraft: A game where you design a robot and then pit it against other players' creations in online team battles. My best creations were a spider bot that could scuttle up and over hills and ambush enemies with a massive plasma burst, and an air defense bot with bigass twin AAGs and a shitload of top armor. I had a lot of fun with this one back in the day, but nowadays it's so deserted that most of the players are bots.
I tried to get into this one twice and bounced off both times, which is a shame, because I really wanted to like it. I found it really complicated and fiddly (why do I need to choose which specific model of truck hauls things between two production buildings when the differences between trucks are basically non-existent?) and the tutorials unhelpful ("follow these steps to set up a power line. How do you know which kind of power lines you need? What do these gauges mean? We're not telling you, onto the next tutorial!").
I had to watch a few (long) tutorials and play along with them to get the hang of it, but want to get back to it. The "Realistic Mode" was the coolest to me, I'm so sick of city builders where the only factor is how many $ are in the bank.