I had an OG nGage when they were still (as close as they would ever be to) relevant; I won it as a prize in a competition. And while I really liked it, I wouldn't have bought one with my own money unless the price had dropped by at least 50%, and even that's only given my personal positive experience with using one. As a regular consumer paying full price, it would certainly have been a hard pass for me.
The design seems to have been created by a group of mobile phone designers who once saw some pictures of a Gameboy Advance. I presume that the astounding decision to put the single game/SD card slot under the removable battery came from thinking that it would still be a phone first, and users would either install an SD card as a semi-permanent upgrade, or keep one game in the device until they finished it. I've only played one nGage game on mine (Tomb Raider), and the performance wasn't awful but it definitely left something to be desired. They were probably leaning hard on realtime 3D as a way to differentiate it from the GBA, but I don't think the CPU had quite enough power to make it responsive enough.
That being said, I used it happily for years as my main phone, and it generally outperformed all of my friends' phones by a wide margin. The only problem I ever had with "side talking" was having occasional random idiots on the street pointing and laughing. Now we all hold big, flat slices of bread up to our heads, but everyone does it so it's OK I guess. The phone call quality itself was crystal clear both ways. The speaker call mode was also miles ahead of any other mobile phone I saw at the time (or even any phone I've had since). I did get used to using it from my pocket with a microphone headset, though.
The nGage was a high-end Symbian Series 60 device with features much closer to modern smartphones than the more traditional, dedicated mobile phones that formed most of its competition. When it came out, BlackBerry was only just starting to expand beyond the enterprise space into the regular consumer market, and Apple's original iPhone (which don't forget was nowhere near as smooth and polished as they are now) was still 4 years away. Using the nGage with a headset actually worked out well since I often used it to listen to mp3s, a feature that many mobile phones still lacked at the time.
I could (and frequently did) surf regular, unfiltered, uncompressed websites on my nGage at a time when very few portable devices had that capability. And while I didn't play nGage games with it, it was fantastic for playing J2ME and Symbian games, many of which offered a GBA-like experience (albeit on a smaller screen) thanks to the relatively powerful CPU. That's not hyperbole; I was often also carrying a (frontlight modded) GBA around during that period, and switched my on-the-go gaming between them depending on my mood and what games I'd got recently. It also had surprisingly good battery life, although this may have been shortened when playing nGage games.
The nGage gets a lot of flak as a handheld gaming system going up against the GBA, and that definitely wasn't any kind of fight at all. But it was an extremely capable phone for the time, and even as "just" a phone, it still had useful gaming leanings. I think that there was a lot of knee-jerk reaction about "side talking" at the time, and despite there also being some legitimate complaints (like the card slot placement), I feel that it's doing a disservice to Nokia's engineers to have it go down in history as a total, unmitigated disaster.
