Well, I don't know much about the DIR-825, but I would expect from what little's been published that it's a DIR-855 without some bells and whistles, such as the very slick but, in my case nearly superfluous, comprehensive display on the device.
In any case, I'm delighted with my DIR-855 A2 with firmware level 1.11 installed. It's fast, including its html interface, it's reach is unprecedented in my experience and, best of all, its behavior so far (after a couple of months in a relatively heavy mom-and-pop business environment) is flawless.
Let me repeat that. The behavior of our DIR-855 has been flawless. In other words, the DIR-855 can be run indefinitely, at least if our experience is any indication, without rebooting and without any untoward effects.
Now, I've owned a lot of home routers and installed a great number of others for clients, friends and family members. My first home router, purchased in 1999, was a D-Link DI-704, the world's first four-port home router and the product which single-handedly (if you discount the cute, transparent DI-701 introduced nearly simultaneously) created the home router market. The DI-704 also performed flawlessly and, in the early years, I purchased several more for friends and family, one of which is still in daily use.
But until I installed my new DIR-855, I hadn't found another one which operated quite as flawlessly. I replaced my DI-704 and wireless access point with a DI-624 when I upgraded from 1.2 megabaud ADSL service to 28 megabaud cable service and discovered the DI-704's 3.5 megabaud speed limit. I replaced that with a DI-784 which, after some time, fried. D-Link had just announced a new router, so I ran out to Comp USA (which was still thriving at the time), Best Buy, Circuit City and a couple of others and found nothing. No D-Link routers at all. So, I bought a Linksys WRT54GX Draft-N router at Staples. But I immediately returned it as I found that Linksys still didn't realize that their embarrassingly rudimentary DHCP server has no provision for IP address persistence, something which is necessary in a server environment. In fact, to the best of my knowledge, Cisco still doesn't include IP persistence in their Linksys routers, reserving this feature that most others consider essential for their Cisco-branded professional products. I returned that router immediately and bought a Netgear WPNT834, including, in my opinion one of the worst bits of firmware ever written. I had loads of problems with that turkey, the worst being that it rebooted itself when traffic levels were high, something Netgear Customer Service actually defended! I persisted for a couple of months, trying to get Netgear even to admit that the product had issues. I gave-up, demanded and, following threats and a lot of pain, received a full refund from Netgear. I replaced that with a Buffalo WZR-G300N, which also had severe firmware problems and also could not handle our modest traffic load (it works well, however, in a non-server environment, so my in-laws are using it, now). I replaced the Buffalo with a D-Link DIR-635, which was a great relief, to say the least. But the DIR-635 has 100 megbit wired ports. I have an inexpensive D-Link five-port gigabit switch and a laptop with a gigabit NIC. I stream video to my HDTV via the laptop and wanted the fastest connection possible for streaming, so at long last, I replaced the DIR-635 (which still works perfectly) with my DIR-855.
I think "all the trouble the 855 has had" that you refer to involves the original A1 units and those which had their antennas wired incorrectly at the factory. The good news is that, as far as I know, my excellent experience with the A2 version DIR-855s now being shipped (in small numbers, alas) is typical.
The bad news is that, contrary to my experience of the past with D-Link, their customer service policy clearly has become warped. I don't include the D-Link helpers in this forum, for they are greatly appreciated. In any case, D-Link no longer answers my e-mail and, when phoned, are likely to tell you anything they think of, true or not. For example, when I was trying to find out this Spring when the DIR-855 would be shipping again, I was told by a D-Link representative that the model didn't exist and had never existed, all evidence to the contrary.
Still, given the choice, I'd rather buy a nearly perfect product from a company with bad customer service than a flawed product from a company with good customer service, not that any of the outfits in the home router market presently that I've dealt with lately does any better. Everyone is struggling in this miserable economy, and perhaps the general decline in customer service is merely a reflection of resulting staff reductions. At least D-Link is still capable of producing superlative products, even in these exceedingly hard times.