I personally liked AOFR more than Oathmark. Oathmark is not a bad game by any means, and I think that it generally does what it was intended to do rather well (collect all of your miniatures from different races and put them in one army with no houserules). However, after playing roughly 8-10 matches with it (primarily Orcs and Humans VS The Undead - the same composition remains true for OPR, since it's the same opponent) we were mostly done and were willing to switch to another system due to some of the game's quirks that became very apparent in the last few matches.
1. The main mechanic of only ever using five dice regardless of the models' quantity immediately breaks once you have vastly different quality levels on the field. Once heavy cavalry, brutes and dragons are present, normal infantry becomes absolutely useless - they get wounded on something like 3+ with good chance of dealing double wounds per strike while struggling to get a single point of damage in return. I get it that the author probably didn't want to turn the game into throwing down buckets of dice, but capping attacks at five simply doesn't work when you have a single dragon with Fight 8/Defense 14 annihilating almost infinite numbers of Fight 2/Defense 10 spearmen. The game thus heavily skews into elite units that can easily take out 2x-3x their cost in points and still live, sometimes at full health. Yes, they are more expensive, but why do I care if you simply can't even wound them most of the time? Once we realized how much heavy artillery, dragons and knights were dealing in terms of damage, the game became very stale. Without any monsters, however, the game's speed of play greatly diminishes, as it's just two similarly inept forces pushing each other around for multiple turns.
2. Units' profiles can be a bit stale - for some reason the author is heavily against more fantastic elements in the game; even halflings were a rather late and, to be frank, underwhelming addition. No daemons, cave dwelling races, ratmen, East-inspired mythological creatures and the like. Core armies' troops are very similar, often differing by a couple of stat points - there aren't even any crossbows, almost everyone uses the same 20" bow, with Elves receiving +2" of range and that's it.
3. The Undead's faction mechanic is very awkward and poorly balanced - they are almost immune to normal shooting but quickly turn into dust once in striking distance. Not fun both for me and my opponent. Also, Burrow Worm is a prime example of flat out bad game design from my point of view. Imagine a unit that immediately wipes the floor with anything it touches and doesn't actually cost much, but its main weakness is that you won't even be able to actually use it for 70% of the game. Such a proposition is inherently impossible to balance and reeks of old
GW's favourite "Roll
2D6, on 2-11 nothing happens, on 12 you may immediately destroy 50% of the opposing army".
4. It's a very minor gripe, but I still have no idea for whom the water-themed supplement was made. Are there any wargamers with half a dozen barges capable of taking 20 men strong ranked units aboard, waiting for a chance to play Warhammer Fantasy in a pond? Such a bizzarre addition.
AOFR, in comparison, is very aggressive and fast, it has way more interesting and diverse faction rosters (although not nearly on the level of
GW games, but I will probably put forth an unpopular opinion and say that
GW game design is pure insanity). I will notice that I've also read Grimdark Future and Age of Fantasy Skirmish rulesets and found them to be too simple to catch my attention, but AOFR significantly changes things by making flanks matter since a flanked unit doesn't return strikes at all, and can be destroyed even if it received minimal losses. The act of actual maneuvering is also quite forgiving, the game doesn't overload you with excessive details. Playing Vampiric Undead and Orcs is a pretty different experience, since we both have to watch out for different things from the opposing army (I need to shut down morale-reducing Ghoul leader, my opponent has to be aware of my Brutes getting a successful charge into his light infantry blocks). The factions are also quite diverse, so you can build a lot of different lists even within single race. Unfortunately, we have only managed to get a single game in since 3.0 dropped (which I've lost disasterously), but I personally regard the changes to its base ruleset as positive and looking to try it out more in the future. Also, OPR Army Forge is awesome, very reliable and easy to use, it's a major upside for anyone wanting to give their systems a try.
We like AOFR more than Oathmark, however, it's not without its faults.
1. The balancing can be rough at times. With several hundreds of official (and several hundreds more of semi-official and fanmade) unit entries it is to be expected, but some of the profiles are vastly superior to the others for similar costs. My main gripe are brutes, i. e. medium monsters like Ushabti or Trolls - they pack way too much punch for their cost and are almost always point-for-point superior to normal infantry. On the other hand, "elite" heavy infantry like dismounted knights are still not that useful and are very prone to sudden losses due to them being very expensive, but still one wound models. Point tax for applying different rules to a unit is also a bit inconsistent - Men at Arms are strictly worse than Orc warriors in every possible way aside from re-rolling failed Morale rolls (provided both units are led by stat-increasing leaders), but they end up costing more, and you don't actually need to reroll failed Morale rolls if you just simply win the actual fight (that Orc warriors achieve more reliably) and thus have no need to test at all. 3.0 mostly fixed cavalry trampling literally everything else on a successful charge and busted large monsters so I have hope the developers will eventually figure the remaining issues out.
2. The game's core scenarios are very mundane, it basically begs of you to invent your own battles. Default 4 turns is not nearly enough for big armies to finish their business, so we usually play either 5 or 6 and sum up both secured objectives and kill points - it's a very minor addition but increases the scenario's complexity dramatically.
3. The magic is a bit stale. 3.0 brought some interesting changes to how casting works, but majority of spells are way less interesting than Oathmark - 90% it's stat increase or decrease, and I would like for OPR team to try something new.