edit: Is Battlefield 4 worth buying on sale complete for $20 game+dlc included or the $5 for the game alone?
Did you actually add BF4 during (Free) Game-Time? Sometimes EA puts that game (and others) on their Free "X amount of hours or day" Game-Time Campaign (they've done it w/ SW: Battlefront by DICE, Titanfall, BF4 + Sims 4). You really should add them, when they do - b/c they are Free Trials are for the full entire base-game normally for a certain amount of days when you decide to first launch the trial (which is so totally up to you when you do it - I still have free Game-Time trials for SW: BF and Sims 4 sitting in my Origin account, from when they first added them).
...
Actually, BF4 is on Game-Time: so add it, see if you actually dig it before you decide to buy:
https://www.origin.com/en-us/store/free-games/trials
I think this all w/ buying BF4 really depends on the amount of mileage you expect to get out of BF4, depending on if you should go for Complete or Base-Game only.
BF4 SP campaign should take about 5-10 hours per playthrough; depends on what difficulty you throw it on, how you feel about the new leveling/progression system; and (of course) how good you are at it. Personally, I had a blast with it and found it to be one of the better BF SP campaigns since BC2. It certainly was better than BF3's campaign, IMHO. Just don't expect a stellar story or character development - it's the non-stop action here for why you're playing. B/c of how weapons now unlock + the experience system here (yeah, there actually is a leveling system here...in the SP campaign) are much different from previous BF games - for some who like the campaign, this unlock + experience system might make the SP campaign even more re-playable than before.
BF MP is BF MP. This is usually what most people really play BF games for -
b/c their MP is usually stellar. And with patches behind it and not being the mess it was said to be at launch: BF's finally good; damn good. If you've ever played BF before, you know this: you're going to have to use teamwork, in most game-modes - it's the way these games were ALWAYS built. If you don't use teamwork, then...well, expect to lose. I've always had fun w/ the BF MP's - the chaos; the action; the vehicles; the gorgeous graphics technical quality on their engines.
Even though most likely, when I buy a BF game - just about everybody else is high-leveled in the MP, I haven't played the game enough to get good at it, and I'm way down there as a newbie scrub in terms of level-wise. I usually get a fair 5-10 hours at least out of their MP portions. After a while, for me - competitive MP is competitive MP; and I grow tired of it. I certainly got more hours w/ BF2: BC + BF3's MP, as those was really my first BF games and it felt very new to me; MP formula ain't really change super-duper much over the years, TBH.
I hope when some of the BF4 DLC's + Hardline DLC's were free before on Origin during On The House, you caught them. Always add the free DLC stuff when they do them "On The House" (for that limited time) to your Origin account, even if you DON'T own the base-game - b/c Origin will actually let you add DLC's to activate them to your account even before you own the base-game (unlike Steam). IMHO, Origin gets this thing (Add DLC before you own base-game) right over Steam [it's probably one of the very few things I like about Origin] - b/c this stuff can entice me more so to buy the base-game quicker, especially if they've given me free DLC's or priced DLC's cheap.
I actually bought BF: Hardline [base-game] from Origin for $5 over the weekend (75% off before tax). Will do SP Campaign impressions + look at the MP (if anyone's still playing the MP), when I actually get to playing it.
This is the cheapest BF: Hardline has been, according to ITAD:
https://isthereanydeal.com/#/page:game/info?plain=battlefieldhardline