The downsides of a LGA 775 system:
1. Processor: Your processors from the LGA775 chipset lack many modern features, with the most impairing features being: Lack of L3 Cache, lack of hyper-threading, lack of instructions, most notably SSE4 and AVX, which are becoming more common in modern games and applications. These processors alone should now be considered obsolete as of 2018 - 2019, where the transition of SSE4 and AVX in games is becoming more prominent. From a workstation standpoint, you can't even use these processors for modern tasks, and from a desktop standpoint (which should be considered web browsing, emails, etc.) it's just barely functional compared to a modern processor.
2. Motherboard: LGA 775 motherboards lack USB 3.0 and SATA III to name a couple features, and these two are probably the most hindering. SATA II speeds, even with a SSD, can cause SERIOUS bottlenecks in video games that require a lot of data to be loaded on the fly, GTA V for example. And without a fast USB 3.0 interface, you will have a hard time using external media and USB 3.0 devices, making the transferring of files or even backups feel like you're in the cartoon with the Flintstones. While there are PCI-express adapters you can use, most notably for SATA III, the cost of such a device in one of your precious PCIe slots may be hard to swallow.
3. Memory: Most LGA 775 motherboards only allow up to 4 GB with some of them allowing up to 8 GB. And the transfer speeds of these DDR2 modules are a bit low, so if you only have 4 GB, see above about the Flintstones if you plan on gaming. If you have 8 GB, you're almost in the clear, just remember, the RAM is SLOW, which will reduce your FPS in some games, and some games require 16 GB, which means even if you could play a game, you're left out of the fun because you don't have enough memory.
4. Chassis: Let's just throw this in here as well. Most LGA 775 systems have an ancient, ugly, silver case with no kinds of air filters or cable management. That means, spaghetti wires everywhere, dust everywhere and terrible airflow. Not what the PCMasterRace had in mind.
5. Price/Performance: Some people may argue that the prices of an LGA 775 system are so low it may be worth the buy. I can assure you - it's not. For roughly $300 - $400 USD you can build a cheap system using a Dell Optiplex 7010 MT ($100), i7-3770 ($100) a 500W Power supply ($50), and slap a GTX 1060 in ($150) and you're able to play all the latest games. Maybe you can even find that above system for cheaper (eBay). The point of the matter is, even if you are getting all of the parts for around $50 - $100, just remember, you don't even get a fraction of the performance of a newer system. (The above system isn't even all that much newer, ~5 years)
